1. Flexible Supports – Ian Rowlands
2. Rigid Supports – Ian Rowlands
3. How to Stretch a Canvas – Ian Rowlands
4. Size Preparations – Ian Rowlands
5. Priming – Ian Rowlands
6. Oil Mediums – Ian Rowlands
7. Oil Based Mediums – Ian Rowlands
8. Varnishing – Ian Rowlands
9. Oil Colour Facts and Figures – Ian Rowlands
10. Dark Matter: recipe for White Bone Black
– Jo Volley
1. FLEXIBLE SUPPORTS – Ian Rowlands
Flexible or non-rigid supports for oil painting are those which need to be stretched over a frame for work and display. They are more popular than rigid surfaces despite the fact that their preparation is more complex and that they are more susceptible to damage from mechanical and atmospheric sources. Their popularity is due to their lightness in weight for use on a large scale, and to the surface quality, which the chosen fabric contributes to the painting.
Think of a flexible support for oil painting and you will inevitably come up with Canvas. This is a generic name given to strong and closely woven fabrics such as cotton, linen, and synthetic fibres.
Regarded as a superior fabric for oil painting, Linen is made from the fibres of the flax plant, and is characterised by its greenish-brown colour and irregular texture. Its appeal lies in the irregularity and natural quality of its surface and the rigidity and strength which is provided by its long fibres. However it is fairly expensive and needs careful selection and diligence in its preparation for painting.
The high cost of the fabric is partially explained by its lengthy manner of production. In order to retain the long fibres the flax is pulled from the plant rather than being cut. Following the removal of the seeds the flax is allowed to decompose in warm water tanks in order to break down the pectins that hold the fibres together. Before spinning the fibre is mechanically separated from extraneous woody matter resulting in a mixture of fibres of two lengths, short ones known as ‘tow’ and long ones called ‘line flax’, which are separated by combing. How the linen is spun will affect its texture as a fabric.
Dry spinning produces a fabric with a fuzzy texture, whereas wet spinning produces one with a smoother, harder surface. Canvas produced with wet spun line flax making up the warp and weft of the fabric is a vastly superior product, both in terms of durability and texture. The warp fibres are those which travel the length of the fabric, whereas the weft fibres run across it. Before purchasing linen it is a good idea to hold it up to the light and check that the warp and weft are made from fibres of an equal thickness.
A disparity between the warp and weft tends to cause problems associated with uneven tension such as cracking. You should also note the openness of its weave; a canvas with too open a weave is liable to be weak, unpredictable during priming and is best avoided. The density of the weave is expressed in threads per inch, the greater the number, the denser the weave.
Artists have used Cotton Duck, a more recent addition, since the 1930’s. Cotton has a more uniform texture than linen and the best grades are tightly woven. It is less strong and more elastic than linen being made up of shorter fibres known as staples. In lower weights and lesser qualities, the elastic nature of the fabric can be a problem making its recovery from dents poor. These have to be removed by carefully dampening the reverse of the canvas around the dented area. The best grade of cotton, Sea Island, comes from the United States and has longer staples imparting more strength and reducing elasticity. The method of harvesting is purely mechanical and involves separating the cotton fibres from the seedpods. Reservations aside, cotton is easier to prepare than linen and brings canvas within the reach of all of us.
Cotton duck should also be inspected prior to purchasing paying attention to serious flaws and vegetable matter caught up in the weave. It is available in many weights but is best avoided in weights below 12oz, which are usually too open and flimsy. A tightly woven, high grade 15oz cotton will give you a very stable surface. These fabrics are offered to us as raw materials, ready primed, or as ready stretched surfaces. How we purchase them will depend on our time and budget. One advantage of preparing your own canvas is that, with a bit of practice, it is possible for you to achieve the surface you require rather than a manufacturers idea of this. To get started you will need to decide upon the fabric with the best texture and weight for the task. A smooth texture is useful for detailed or small work whereas a rough texture will encourage the build up of paint and is more suited to larger work. The weight of the canvas is measured in ounces per square yard or grams per square metre and is of great importance being influential on its strength. Large paintings need a strong, heavy surface, whereas small paintings can be carried out successfully on lighter weight fabrics.
Once you have selected your flexible surface you will need to stretch it before working on it. For this you will need a set of stretcher bars. These are usually made from kiln dried pine and are machined with bevelled edges and mitred corners with mortice and tenon joints for easy assembly. Keys or wedges can be inserted into each joint in order to expand the stretcher and tighten the canvas if required at some later stage. The bevelled outer edge lifts the canvas away from the inner edge of the stretcher preventing ridges forming during sizing and priming. Some suppliers use an additional lip to lift the canvas even further away from the bars. Stretchers are available in several sections. As a guideline I would recommend 1in for work up to 12in; 1in for work up to 18in and 2in for work up to 48in. For sizes larger than this a 2in section should be used to ensure stability. If the work is larger than 36inches in any one direction it will be necessary to add a crossbar; beyond 40 inches it is wise to use bars each way. To assemble your stretchers make sure you have a clean and uncluttered area to work in. Lay the stretcher pieces out and check that the bars are the correct way round and that the bevels face in the same direction. Using a mallet, not a hammer, knock the stretchers and any crossbars together to form a square or rectangle. Using a tape measure or a piece of string, check the squareness of the frame by measuring diagonally across the corners. The frame is square when both measurements are equal. To prevent any movement during stretching put a temporary staple across each mitre before proceeding any further. On a flat, clean surface, lay down the fabric and place the stretcher upon it with the bevels facing down. Line up the weave of the fabric with the edges of the frame and cut the cotton or linen, allowing a margin of 2 inches (5 cm) around for securing to the stretcher. Using a tape measure, mark the halfway points along the edge of each stretcher, and then at 2in intervals towards each corner. These mark the points at which tacks or staples will be placed and accuracy at this stage will ensure an evenly distributed tension. With finger tension, pull the fabric to one of the halfway points on the stretcher and fasten with a staple or tack, repeat this for the opposite side and then for the halfway points on the remaining two sides. There should now be a diamond pattern of tension on the fabric. Ease the canvas towards each of the corners fixing with a temporary staple or tack on either side of the mitre. Along one of the edges and working from the centre, pull the fabric and secure on each of the marked points, stopping just short of the corner. Rotate the canvas through 180° and repeat the previous step (diagonally opposite). Keeping the stretcher the same way up, complete the edge, working towards the other corner. Finally complete the remaining section of the opposite side. Repeat to complete the remaining two sides of the canvas. Remove the temporary tacks or staples and secure each of the corners by making two folds, pull one over the other and tack or staple. The following points should be observed.
- Linen is a sensitive fabric prone to shrinkage and should not be stretched but attached loosely to the stretcher prior to sizing. The force of shrinkage of linen is sufficient to break a stretcher. When using acrylic sizes and priming, where the fabric tends to relax after initially tightening, my recommendation is to use thumbtacks for all securing, replacing them with tacks or staples after sizing and priming, as restretching is usually necessary at this stage.
- In order to place less strain on the fabric and stretcher the warp threads of linen should travel across the shortest distance on the stretcher wherever possible. During weaving the warp threads become tense and as a result are more prone to shrinkage and slackening than the weft.
- Acrylic priming sometimes relaxes cotton duck, rather than restretching at the end, you could put in tacks or staples at 4in rather than 2in intervals, then pull and staple between them once the priming is complete.
The method for stretching primed canvas is the same as for unprimed except that greater force is needed to get the required tension. In order to do this, canvas pliers are used and the staples or tacks are fastened along the side edge of the stretcher in order to gain sufficient tension.
The canvas is ready to be sized and primed.
Sizing & Priming
Sizing and priming perform two important functions. Firstly, ensuring the ideal conditions for paint to be applied, providing a surface to which it will bond. Secondly, forming a barrier that protects the fabric from the injurious effects of the oil that may be contained in the colour.
For cotton I would recommend only using Acrylic primers; they are far safer than Rabbit skin glue on this elastic fabric. The first coat should be diluted with water to enable it to flow easily across the surface. Following this the surface should be sanded lightly with a fine abrasive paper. Two or three coats of primer should provide you with a good surface.
When preparing linen the decision is not so simple to make. For many years I have used traditional size followed by oil-based primer of home made or bought in variety, this has given me the required surface. However, it is a fact that size absorbs moisture and swells as a result, shrinking when the atmosphere becomes drier. This constant swelling and shrinking sets up tensions that can lead to cracking of the size, the priming and subsequently the paint layers. There are two ways of dealing with this problem. The first is to use the glue at a much weaker strength than we are accustomed to. I recommend a ratio of 1: 30 (glue: water), by volume. By using the glue in this way we are reducing its thickness and therefore the moisture absorbency of the linen. Weaker glue also impregnates the canvas rather than sitting on the surface, this is also safer. I use a small natural sponge to apply the size as it gives a good even coat without overloading the fabric. Two coats of weak size are sufficient to do the job. The linen can now be primed with an oil-based primer. Alkyd primers have virtually replaced traditional oil grounds, drying quickly, they remain more flexible and are virtually non-yellowing. It is a good idea to allow this type of ground to mature for several days before starting to paint.
The second way is to abandon traditional grounds and use acrylic sizes and primers, which actually seal the fabric against moisture and therefore reduce the risk of future problems. The acrylic primers also size and prime in one process and so are more straightforward to use. The difference between Acrylic primer and Gesso, is that the latter contains more solid material and is more absorbent. This absorbency can be controlled by using acrylic size first or by adding a small amount of a compatible acrylic medium to the gesso. It is best to consult the individual manufacturers information on this subject.
2. RIGID PAINTING SUPPORTS – Ian Rowlands
Paintings were carried out on rigid surfaces, such as caves, walls and panels long before the adoption of flexible fabric supports such as canvas. The use of rigid supports dominated European painting until the high renaissance when much larger scale works would have made the use of panels impractical. The masters of the early renaissance did not necessarily have easy access to the materials required to construct panels. Geography, and obviously availability, largely dictated the type of wood used by an artist, especially before the days of manufactured materials and rapid transportation. Italian artists tended to use Poplar, which grows rapidly to sufficient size to yield large planks which were joined together to form large sheets. However Poplar suffers from many defects: soft erratic grain, susceptibility to damage from woodworm and a tendency to warp. The better quality woods were unavailable due to deforestation and their use for shipbuilding. North of the Alps the situation was considerably better, a greater variety of woods were available with oak being the most favoured amongst Flemish, French and British painters. Nowadays we have the benefit of a much greater choice of rigid materials, home produced or bought, on which to carry out our paintings and these offer us many advantages not enjoyed by earlier painters.
Modern panels are relatively inexpensive and sold in large enough sheets to make joining them unnecessary. They are a cheaper alternative to canvas, particularly on a small scale where the use of battens is not necessary. They are quicker and easier to prepare than canvas, especially if an acrylic primer is used. As rigid surfaces flex less than canvas, they are safer when using paint films containing a high percentage of wax based mediums. The same is true of paint applied with a painting knife, whether applied thinly or thickly, where slight flexing or a rear impact could cause cracking. Collage and mixed media works are more safely carried out on a rigid surface, as are works involving gilding, incising and scraping.
I would recommend that you do not consider solid wood as an option, it can be expensive and its moisture sensitive structure tends to cause warping or cracking. I would instead use the following modern alternatives available which are, lighter, cheaper and easier to prepare.
Plywood, a laminate of several layers, often of different types of wood, is available in large sizes and various thickness. Thin layers of veneer are shaved from a rotating log, much in the manner of a pencil being sharpened. The layers are glued together in a sandwich, each with its grain at right angles to the previous layer in order to counteract the stresses that could cause warping. Exterior grade plywood offers the best moisture resistance but interior grade tends to have a finer surface. inch ply is suitable for small panels whereas large panels may require a 1inch thickness. Any panel larger than 25 inches in one direction will require bracing but this is a simple matter. Using PVA based wood glue, attach battens to the rear of the panel securing them with ‘G’ clamps until the glue is firm. Once all sides are battened and the glue has dried, the panel can be primed, including its sides to prevent ‘delamination’ ( the separation of the different layers of veneer. You may also glue a layer of either muslin or fine canvas to the face of the panel to prevent any swelling caused by absorption of moisture. This swelling could cause shearing away of priming or a pattern of cracks consistent with the grain of the wood. The fabric may be left visible or concealed by the priming which overlays it.
More straightforward to prepare than plywood, composite materials could be considered your best option: Hardboard and MDF are the two most widely used. Hardboard is made from steam exploded wood pulp which has then been compressed and reformed into a single layered sheet, it is held together by a natural adhesive found in wood called lignin. The resulting board, with its smooth front and textured rear, is a very good material to construct painting panels with. It is available in inch and inch thickness, in sheets measuring 8×4 feet, large sheets should be braced in the same manner as plywood. It is fairly light in weight and its front surface is smooth enough with simple priming to provide an excellent painting surface for detailed work. MDF ( Medium Density Fibreboard ) is one of the most stable panel making materials available, its surface is smooth and tough, and apart from its edges it has excellent moisture resistance. Its process of manufacture is similar to that of hardboard in that it is also a reconstituted wood product, but it is held together by urea-formaldehyde resin. It is available in ¼ – 1¼ thickness, in sheet sizes up to 5×9 feet, but it is a heavy material and because of this I would not recommend its use for large pieces of work. As they may not be stored in ideal conditions before sale, and will have been handled, both hardboard and MDF should be degreased, prior to sizing and priming, using methylated spirits. Acrylic-based primers or gessos are simple to use and allow you to devote your energies to painting rather than perfecting grounds. It is on rigid supports that acrylic priming systems are particularly effective and I would advocate their use in all but a few cases and for several good reasons. They perform the task of size and primer and therefore save you time. They seal the support against moisture, unlike rabbit skin size, which tends to attract it. Rabbit skin glue can vary in strength from supplier to supplier, and even batch to batch, whereas acrylic primer is consistent and if used according to instructions will give reliable results. Acrylic primer can be applied by brush or rollers giving you a variety of textural variations. Lastly, because they are waterbased, Acrylic primers reduce your exposure to volatile substances, both in use and for cleaning up.
3. HOW TO STRETCH A CANVAS – Ian Rowlands
Cotton duck or linen
Staples or tacks
- Assemble the stretchers by joining the morticed corners that are diagonally opposite each other. Join the two ‘L shaped’ sections together to form a square or rectangle. Check to see that the bars are the correct way round and that the bevels face in the same direction.
- Check the squareness of the frame by measuring diagonally across the corners. The frame is square when both measurements are equal. Once the frame is square, put a staple across each mitre to prevent any movement during stretching.
- Cut the cotton or linen, allowing a margin of 2 inches (5 cm) around for securing to the stretcher.
- On a flat, clean surface, lay down the fabric and place the stretcher upon it with the bevels facing down, the rear, flat surface, facing upwards. Line up the weave of the fabric with the edges of the frame, this vital to achieve an even tension.
- 5. Using a tape measure, mark the halfway points along the edge of each stretcher, and then at 2-inch intervals towards each corner. These are the points at which tacks or staples will be placed.
- 6. If using cotton duck, with finger tension, pull the fabric to one of the halfway points on the stretcher and fasten with a staple or tack, repeat this for the opposite side. Turning the frame, secure the other two halfway points. Along one of the edges, pull the canvas towards one of the corners and fix with a temporary staple or tack, repeat to secure the other corner along the same edge. Secure the corners of the opposite edge in this way and then repeat the process for the other two edges.
- 7. Along one of the edges and working from the centre, pull the fabric towards the edge of the stretcher and secure on each of the marked points, stopping just short of the corner. Rotate the canvas through 180° and repeat the previous step (diagonally opposite). Keeping the stretcher the same way up, complete the edge, working towards the other corner. Rotate the canvas through 180° and complete the last section of the opposite side. Repeat step 7 to complete the remaining two sides of the canvas.
- 8. Remove the temporary tacks or staples and secure each of the corners by making two folds, pull one over the other and tack or staple.
The canvas is now ready to be sized and primed but the following points should be observed.
• Linen is a very sensitive fabric and should not be stretched but attached loosely to the stretcher prior to sizing, this is particularly crucial when using acrylic sizes and primings, which tend to relax the fabric. My recommendation is to use thumbtacks for all securing. These can be replaced with tacks or staples when sizing and priming are completed.
• Acrylic primings also tend to relax cotton duck, so an alternative fastening pattern can be used. At step 7, tack at 4 inch rather than 2 inch intervals, then complete the latter once the primings are complete.
4. SIZING – Ian Rowlands
*Rabbit skin glue
Rabbit skin glue granules
Double boiler (or similar)
Soak the granules in cold water for at least 2 hours.
A guideline for proportions would be:
Canvas sizing 1 : 30 (granules : water)
Chalk ground 1 : 15
*Half chalk ground
Heat the soaked solution in the top chamber of the double boiler until the size has melted (no granules are visible). Take care not to overheat and cook the solution, the lower part of the boiler should only brought to a simmer.
Apply to the support, hot for hardboard, plywood and MDF; blood temperature for canvas, paper and sundeala board.
Double boilers are expensive. A cheaper alternative, and one that retains heat without scorching the solution, is a pudding basin over a small saucepan.
Glue strengths can vary a great deal from supplier to supplier. It is worthwhile to make notes when preparing the solution, paying particular attention to its characteristics when cooled.
For sizing rigid surfaces the cooled solution should be a firm jelly; whilst for flexible surfaces such as canvas it should be a weak jelly which is easy to stir to an apple sauce consistency.
Strengths given are a guideline, experimentation and attention to detail are the key to success.
Lascaux Acrylic Size
Spectrum Copolymer Matt Emulsion (suggested and used by Lisa Milroy)
The above are three examples of modern materials that can be used in place of animal based sizes in certain situations. Although they are intended for use in acrylic based systems they can be used in conjunction with commercially produced oil primers although it is advisable to use acrylic primers over acrylic sizes.
PVA is prone to deterioration and should be avoided.
Acrylic priming systems are easier to use; unlike traditional materials, their properties are predictable, strengths do not vary from batch to batch and the entire process is speeded up.
5. PRIMING – Ian Rowlands
Gesso ground for panels
Glue size (1: 15 water*)
Prepare a small quantity of size by soaking the glue granules in water until swollen. Warm the glue in a double boiler or better still, a Pyrex glass basin, until melted. Remove from the heat source. Add a small amount of whiting to the size and stir gently with a wet hog’s hair brush. Test the mixture by painting onto a piece of waste wood; it should coat it with a milky film. Allow to dry for 12 hours.
Prepare a fresh batch of size (but this time with larger quantities) and melt as before. Start to add the whiting by slowly slipping it into the warm size; the solution will take a surprising amount of whiting. When the level of whiting is just below the surface of the size, and no more can be added, the correct amount has been added. This is easier to gauge with a glass basin. Resist the urge to stir the mixture and allow it to stand for 5 minutes before straining through a sieve into a clean basin. Take a wet hog’s hair brush and gently stir without lifting it out until the mixture feels smooth. The gesso can now be used and should be applied fairly generously, ignore slight imperfections as returning to them can cause the coating to lift away from the panel. Apply 5 or more coats, each time waiting for the previous one to go dull before recoating. In cold weather the mixture may start to gel during application and will have to be stood over warm water to loosen it, if this is necessary add a drop or two of water to compensate for the small amount of evaporation that will occur. Failure to do this will make the upper coats have a stronger glue content and may result in them peeling away. All coats should be applied in one session otherwise the coats will not bond together, so it is just as convenient to make several panels at one sitting.
Allow the panel to dry before smoothing down.
If the resulting gesso is fairly level and free from ridges, it may be sufficient to polish it with a piece of damp cotton until a smooth porcelain finish is achieved. If the surface is ridged it will need to be levelled before smoothing either by sanding or using a cabinet scraper, the latter creates less dust. To use the scraper it should be held almost vertically and pulled towards you following a zigzag or lattice pattern.
To complete the process the surface should be made perfect by sanding lightly with fine wet and dry paper.
The surface of gesso is unlike any other and is the only one that will accept water gilding and true egg tempera.
*Based on Kremer pigment Rabbit skin glue (code 63020)
Chalk ground for panels
3 parts whiting
1 part Titanium white pigment (Optional)
3 parts glue size (1: 15 water)
Sized panel (1:15 solution)
On a glass slab form a well in the centre of the whiting and add the glue size, gradually folding in the powder and work with a palette knife until a firm but glossy paste is formed. If the mixture is too dry it can be adjusted with a small addition of 1:15 glue size, if too wet a small quantity of whiting can be added.
The stiff paste can be stored in a jar and refrigerated. To apply the paste it needs to be diluted to a brushable thin cream consistency by transferring a quantity to a basin adding a 1:30 solution of warm glue size. 2-3 coats of this priming will usually suffice. The surface can be made smooth by wiping with a damp cotton handkerchief.
Half chalk ground for panels and canvas
1 part Titanium white pigment
3 parts whiting
3 parts glue size (1: 15 water)
1 part Stand linseed oil
Sized panel (1:15 solution) or sized linen (1:30 solution)
Mix the whiting with the Titanium white pigment on a glass slab. Form a well in the centre and add the glue size leaving room to float the stand oil on top. Gradually fold in the powders and work with a palette knife until a firm but glossy paste is formed. If the mixture is too dry it can be adjusted by adding more glue size, if too wet a small quantity of whiting can be added.
The stiff paste can be stored in a jar like the chalk ground. It also needs to be diluted to a brushable thin cream consistency by transferring a quantity to a basin and gently warming it through by standing it in hot water before adding a 1:30 solution of warm glue size.
Egg / linseed oil emulsion Ground for canvas and panels
Raw linseed oil
Titanium white (or other) pigment
Rabbit skin glue solution (1:30, glue to water)
Sized panel (1:15 solution) or sized linen (1:30 solution)
Break the egg into a glass jar and shake. Mark the level on the side of the jar and double the existing level with the oil. Again mark the level and double the quantity with water and shake to form an emulsion. This will store for 1 week in the fridge.
Put some Titanium white pigment onto a glass slab and gradually add the emulsion mixing with a palette knife to form a well-mixed, stiff and glossy paste. Dilute the paste with the glue solution to a thin cream consistency. The glue should be warm; hot glue will cook the egg.
Other pigments may be mixed with or substituted for the Titanium white to give a toned ground. The priming should be brushed on very thinly. 3 coats will provide a brilliant white priming.
The Half Chalk and Egg /Oil Emulsion
Grounds can be applied to sized panels and also Linen where it must be applied very thinly and fairly quickly to prevent cracking. The back of the canvas should be supported with some board to avoid pushing it out of shape.
To prime linen, dip a decent housepainters or artist’s varnish brush into the primer by only ¼” so that a sparing amount of it is taken up. Push the primer ahead of the brush by angling it at 45 degrees working in a circular motion to work the primer into the weave, finish off with a light straight stroke to bring it onto the top of the canvas tooth.
6. OIL MEDIUMS – Ian Rowlands
For oil paint to be used effectively some form of medium or vehicle should be introduced during the paintings’ construction. As we have previously seen, oil colour consists of pigment particles evenly dispersed in a drying oil, such as linseed, forming a continuous, tough film. The film is capable of encapsulating the pigment particles and has sufficient adhesive strength to hold each paint layer to its predecessor. When working in layers the integrity of the paint film is upheld if the colour is applied ‘fat over lean’. This is a basic technical requirement of layering; ‘fat’ (high oil content, flexible) colours should be applied over ‘lean’ (low oil content, inflexible) colours. If the colour where to be diluted solely with solvent it would, layer by layer, leave the film increasingly under-bound, with the associated problems of loss of adhesion, brilliance and probable cracking. The adoption of some sort of vehicle helps you to observe the fat over lean rule ensuring your painting has a sound structure, from the ground to the final layer.
The most basic mediums are used to dilute the colour, reducing its consistency, allowing it to flow from the brush whilst maintaining the paint films integrity by replacing some of the binding strength lost when diluting the colour. Other mediums can modify the painting’s appearance, enriching it, adding depth and gloss, or doing the opposite by matting down the surface and creating coolness.
Some mediums can alter the speed at which the paint layers dry. Quick driers that allow glazes to be quickly superimposed, or those that retard drying extending the time when it is possible to blend and soften areas of colour. Finally there are gel mediums that can add texture to the surface of the painting more safely than by using heavy paint. It is probable that some mediums will combine two or more of these properties, allowing increased flexibility in working methods.
Turpentine allows straightforward dilution of the colour; purchase it only from artists’ supply stores to be certain of its quality. The names double distilled or double rectified turpentine are indicators of products suitable for artists use. White spirit can be used in place of turpentine but will produce a slightly drier surface. It is just as good as turpentine as long as it carries the British standard number BS 245. Odourless thinners are probably the most comfortable solvents to work with, especially in a domestic set up. Currently available are Kremer Shellsol T, Jacksons low odour solvent, Daler Rowney low odour thinners and Winsor & Newton Sansodor. Treat all such solvents with respect as they are potentially harmful. Make sure your studio is well ventilated and replace tops on bottles to reduce the amount of solvent evaporating into the air. The aim of diluting paint is just to thin it to a brushable consistency, not to drown it in turpentine, as this would leave a vulnerable film with reduced adhesive strength.
Assuming that the painting will proceed beyond one layer it will be necessary to modify the solvent, fattening it up by adding a percentage of oil to it during the second and subsequent paint layers, increasing this amount as the layers build.
Refined linseed oil is one addition, but I favour Stand oil, a form of linseed oil that has been heat polymerised in the absence of air. It is pale, viscous and if diluted with a thinner dries relatively quickly to form a flexible non-yellowing film. A good mixture, which sufficiently fattens the colour without adding too much gloss, is a ratio of 1:5, Stand Oil to Turpentine (or equivalent solvent), that I introduce into the second layer of paint; the first being diluted with pure turpentine to provide a matt surface on which the second and subsequent layers can grip. I increase the ratio to a maximum of 1:3 for the final layers but a higher proportion of oil would result in a glossy, enamel-like, self-levelling film free of brush strokes. I have used Stand oil for many years and so far none of my paintings using it have developed cracks or darkened.
Besides strengthening the paint film, mediums allow you increased scope for experiment by creating certain optical effects.
Transparent glazes create warmth and depth, whilst semi opaque scumbles create optical blues and greys and cool down the painting’s appearance. Both techniques can be used in the same painting and benefit from a quick drying medium as many layers may be required in order to achieve the desired effect.
A classic quick drying glaze medium is made from a mixture of dammar resin, stand oil and turpentine. Dammar provides depth, lustre and richness, and dries fairly quickly but as it is easily dissolved when over painted; stand oil is added to make the film insoluble. Roberson manufactures such a medium under the name of Roberson Glaze Medium and have recently added a very useful Matt Glaze Medium that unlike other types does not increase the painting’s gloss.
Modern glaze mediums tend to be based on the very reliable Alkyd resin group. Alkyd resins behave similarly to their natural counterparts allowing glazes to be quickly superimposed but have the advantage of forming tougher films less prone to being shifted by the solvents contained in subsequent layers. You are most likely to encounter alkyd resin in ready made products that have been modified by adding oil and driers and ranging from liquid to gel like consistencies. The liquid type alkyd mediums are useful for creating smooth, glossy films that are enamel like; flowing easily from the brush they permit detailed marks. Furthermore they can be thinned with white spirit during the first layers. Although these mediums are classed as for glazing, they can be used to dilute opaquely applied paint, in which case they will accelerate the drying rate and add a degree of lustre to the finish. Amongst these are Lukas Medium 4, Gamblin Galkyd medium, Daler Rowney Alkyd flow medium, Winsor and Newton Liquin Light gel and Liquin fine detail.
Thickened Alkyd gel mediums retain brush marks allowing you to build texture into paintings whilst accelerating the drying rate; safer than applying heavy coats of paint that would dry very slowly. It is important though, not to overdo it with this type of medium, the film may remain soft on the inside whilst drying on the surface and could slump or pucker. I would also caution against adding excessive quantities of gel as the painting could develop a rather plastic feel. Amongst these are Lukas Medium 5, Gamblin G gel and Neo megilp, Daler Rowney Alkyd gel medium, Winsor and Newton Liquin gel, Spectrum Spectragel and Matt Spectragel which has reduced sheen. It is important to use natural resin or alkyd based mediums from the start to the end of the painting, the fat over lean principle still applies here. The first layers can be thinned, but resin rich layers should not be over painted with thinned colour as cracking may occur.
L. Cornelissen & Son Ltd
020 7636 1045
Roberson mediums, Winsor & Newton mediums and varnishes. Spectrum mediums.
A. P Fitzpatrickexpress
020 7790 0884
Mediums, solvents and varnishes from Kremer
Jacksons / Art express
0870 241 1849
Mediums and varnishes from Jacksons, Roberson, Daler Rowney and Winsor & Newton.
Winsor & Newton / Colart
020 8427 4343
Manufacturers and distributors of mediums and varnishes. Available nationwide.
7. OIL BASED MEDIUMS – Ian Rowlands
Damar Varnish 1
Damar resin 1 part
Turpentine 1 part
Place the resin in a muslin bag or tights, secure with string and immerse in a jar filled with the turps, do not allow the resin to touch the bottom of the jar. Wait patiently for the resin to dissolve, (three or more days).
Use a 50:50 mix with turps as a final varnish. Use as is or slightly diluted for the above mediums.
Damar Varnish 2
Damar resin 250g
Follow the previous method.
Damar varnish 1 part
Stand oil 1 part
Turpentine 5 parts
Combine the ingredients in a narrow necked jar and shake until combined.
Wax & Damar resin for encaustic
2 parts Beeswax
4 parts Damar varnish
1 part Turps
Combine all ingredients in a tin can and heat in a pan of hot water until melted. The cooled solution should form a paste.
Mix the paste with dry pigment or oil colours and apply to rigid supports with brush or palette knife.
For encaustic technique the surface should be heated. The paste can be thinned with turps.
Wax, Damar resin and oil for encaustic
8 parts Beeswax
1 part Damar varnish
1 part Stand oil
Combine all ingredients in a tin can and heat in a pan of hot water until melted, stir thoroughly. Pour the molten solution into moulds (pie dishes or several thicknesses of tin foil). The cooled solution should form cakes that can be broken and melted before grinding with dry pigment. Use whilst warm.
The cakes may melted with turps and mixed with tube oil colours.
Larch Venice turpentine medium
1 part Stand linseed oil
1 part Venice turpentine or Canada balsam
1 part Turpentine
Combine and stir all the ingredients in a double boiler over heat until a homogenous mixture is achieved. Canada balsam may be used instead of Venice turpentine. Lower layers may be thinned with turpentine. A medium thin layer takes 2-3 days to dry less for Canada balsam.
2 tin cans
- Make molds for the molten pastel mixture. Fold a 20×16 inch length of foil into three to give a stable wall. Roll around a piece of dowel to achieve a well rounded shape, seal the end and embed into plasticine to hold the mold upright to accept the molten mixture.
- Mix the pigment with a little turps in a tin can that has been crimped to form a spout. Transfer the mixture to a glass slab and work through with a palette knife to form a lump free paste, return to the can and cover to keep moist.
- Melt the beeswax in a clean can by placing it in a pan of water. Warm the wax slowly until melted.
- Remove the wax from the heat and add stand oil at a ratio of 1:3 or 1:4 (oil: wax). These ratios should give a creamy pastel that will harden. If the wax solidifies, return to the water bath for a few minutes.
- Pour oil / wax mixture into the pigment paste, it is best to start with a 50: 50 ratio; if it is not satisfactory the result can be melted and adjusted.
- Pour carefully into the molds, if wells form in the centre top up with more of the mix. Allow several hours to harden before removing the foil.
8. VARNISHING – Ian Rowlands
Once your painting is finished you will want it to appear fresh looking for as long as possible. Varnishing forms a coating that protects the surface by forming a barrier that absorbs dust and pollution. The varnish should be reversible so that in years to come, it is possible to remove it with its original diluent, for example turpentine, enabling the absorbed dirt and dust to be easily removed. With the paintings surface clean once again, the varnish coat can be renewed.
The painting should be thoroughly dry before applying varnish. I advise waiting at least 6 months, but if you have used thicker paint the wait could be longer. Applying a varnish too soon could cause it to mix with the paintings’ surface and remain tacky, proving difficult to remove without disturbing the paint below. The varnish could also permeate the paint film rendering it sensitive to solvents, with the future danger of cracking. After 6 months, test a discreet area of the painting using a cotton bud wetted with turpentine or white spirit; if no colour is transferred it should be safe to varnish the painting. Even if fast drying media such as glazing mediums or alkyd resin based medium have been used, the surface may appear dry but the underlying layers need to mature. With the painting laid flat, and working from a shallow bowl, which allows the excess to be squeezed from the brush, the varnish should be applied with a smooth action.
Spray varnishes are also available and some may find them easier to apply uniformly. They do not require a brush, container or any cleaning up!
Dammar, the palest of the natural soft resins, has the advantage of staying colourless longer than other natural varnishes and is easily reversible in turps.
Modern synthetic resins, soluble in white spirit soluble include Ketone resin and certain specialist acrylic resins. Ketone resins behave very much like dammar brushing out well and bonding to the painting’s surface; they are virtually colourless and appear to have good reversibility. The synthetic resins should have a life of 20 years or more in ideal conditions and their uniform finish and lack of surface tack on drying are particularly advantageous. As well as being protective, a varnish can have an aesthetic function, modifying the painting’s surface to suit your requirements. Varnishing can add gloss to a dull surface, bringing out the richness which the colours had whilst the painting was in progress. Sometimes though, protection needs to be discreet; here a matt or satin varnish is needed. Matting a painting will slightly reduce the richness of the colour; as all matting agents are slightly opaque. Protecting the surface is really the final act in constructing a painting.
9. OIL COLOUR FACTS AND FIGURES – Ian Rowlands
Colour (Colour index No.) Pigment type Transparency Oil content Drying rate
Cadmium lemon (PY37) Inorganic Semi-opaque Low Fast
Cadmium Yellow light (PY37) Inorganic Opaque Low Fast
Cadmium Yellow (PY37) Inorganic Opaque Low Fast
Cadmium orange (PO20) Inorganic Opaque Low Fast
Alizarin crimson (PR83) Synthetic organic Transparent High Slow
Quinacridone Magenta (PR122) Synthetic organic Transparent High Average
Cadmium Red Deep (PR108) Inorganic Opaque Low Fast
Cadmium Red (PR108) Inorganic Opaque Low Fast
Cerulean blue (PB35) Inorganic Opaque Low Average
Cobalt blue (PB28) Inorganic Semi-opaque Average V. fast
Phthalocyanine Blue (PB15) Synthetic organic Transparent High Fast
Prussian blue(PB27) Inorganic Transparent High V. fast
Ultramarine blue (PB29) Inorganic Transparent Average Fast
Titanium white (PW6) Inorganic V. opaque Low Average
Zinc white (PW4) Inorganic Slight High Slow
Yellow ochre (PY43) Inorganic Opaque Average Fast
Venetian red (PR102) Inorganic Opaque Average Fast
Ivory black (PBk9) Natural organic Semi-opaque High Average
Viridian (PG18) Inorganic Semi-opaque High V. fast
10. Dark Matter: recipe for White Bone Black – Jo Volley
Dark Matter is a publication produced for Lisa Milroy’s exhibition IVORY LAMP MARS VINE BONE at Gallery North, Newcastle upon Tyne in March, 2012. Events around the exhibition included a symposium and workshop with the Slade School of Fine Art, UCL, Northumbria University and the Finnish Academy of Fine Arts, Helsinki. Dark Matter documents all three events, with essays by Helen Baker, Riikka Stewen and Lisa Milroy, and represents a collaboration in material research between these three academic institutions. It also includes contributions from Jo Volley and Onya McCausland, Honorary Research Associate 2011-13, and features the Slade Material Research Project. A limited edition of Dark Matter contains a bespoke silkscreen print created by Jo Volley and Onya McCausland. Dark Matter was designed and produced by Northumbria Graphics, Newcastle upon Tyne.
In conjunction with the book launch the Material Museum presented WHITE BONE BLACK, an exhibition of handmade pigments from a single source and a viewing of the Slade Materials Research Project Pigment Library.
“How To Make Various Sorts of Black”
“Know that there are several kinds of black colours. There is a black, which is a soft, black stone; it is a fat colour. Then there is a black, which is made from vine twigs; these twigs are to be burned; and when they are burnt, throw water on them, and quench them; and then work them up like the other black. And this is a colour both black and lean; and it is one of the perfect colours, which we employ; and it is the whole… There is another black, which is made from burnt almonds shells or peach stones, and this is a perfect black, and fine. There is another black, which is made in the manner: take a lamp full of linseed oil, and fill the lamp with this oil, and light the lamp. Them put it, so lighted, underneath a good clean baking dish, and have the little flame of the lamp come about to the bottom of the dish, two or three fingers away, and the smoke which comes out of the flame will strike on the bottom of the dish, and condense in a mass. Wait a while: take the baking dish, and with some implement sweep this colour, that is soot, off on to a paper, or into some dish: and it does not have to be worked up or ground, for it is a very fine colour. Refill the lamp with the oil in this way several times, and put it back under the dish: and make as much of it in this way as you need. CHAPTER XXXVII
You must know what bone is good. Take bone from the second joints and wings of fowls, or a capon; and the older they are the better. Just as you find them under the dining table, put them into a the fire; and when you see that they have turned whiter than ashes, draw them out, and grind them well on the porphyry; and use it as I say above. CHAPTER VII”
Il Libro dell’Arte, Cennino d”Andrea Cennini C14
Bone pigments are made from bone calcined in the presence of oxygen until all organic matter has been burned away.
Place in a kiln at 900c for 12 hours = bone white
Place in an oven at 250c until charred = bone black
Bone white is used for preparing paper for silverpoint.
Bone black has a warm undertone and is semi-transparent which makes it excellent for glazing applications.