3. Take care with Priming

If a priming is faulty then your efforts to achieve desired artistic qualities may be constantly thwarted, and the survival of the work might be irreversibly impaired. Excessively slick or excessively suctive primings are uncomfortable to work on. A slick ground, lacking tooth and possibly absorbency as well, can induce later wrinkling and cracking in the paint film. A suctive ground, with excessive absorbency, will cause the paint to “sink” quickly to a dull and matted surface.

But the exact feel of a good ground is a matter of personal taste, and painters get quite neurotic in their response to its qualities. It is only possible to cater for one’s own preferences here by priming for oneself: ready-primed canvas or fibrous boards as sold in art shops are standardized products that may not be ideal.

The big DON’T here attaches to the use of decorators’ emulsions, undercoats or ordinary primers as used in house painting: these will normally only be durable to acceptable commercial standards, i.e. 5-10 years, and will often present surfaces which veer between the fiercely absorbent and the impermeable. Their use should be contemplated only after prior research, and for specialized purposes.

To take the three common primers again:

Oil-based.

The advice here is fairly broad. It is clear that good drying and robust structure when dry is important for any primer. Lead Carbonate has been the most commonly used. But traditional advice recommended leaving Lead White primings to dry for at least 6 months in good light before painting on them. This somewhat diminished their popularity. Michael Harding, however, has produced a Foundation White which blends Lead and Titanium pigments with comparatively little oil content, which can be thinned with turpentine to ease application, and which in normal conditions can be dry enough to be painted on within a week.

The degree to which the neat primer should be thinned with turpentine before application is, again, a personal matter. The consistency of single cream has been cited as the norm, but some painters might find the resultant surface, when dry, rather too absorbent. But it is important, especially in the case of sized canvas, that the primer is thin enough to be worked well into the weave or grain of the support. And however thin, the mix with turpentine should be consistent, and accomplished on a surface before application, with a palette knife or spoon, in one batch for each coat. It should be applied with a priming brush or with a mottler in a systematic, area-by-area fashion, so as to avoid the unevenness resulting from evaporation of the turpentine.

Some painters will prefer two coats. In this case, the dilution with turpentine of the second coat should not be greater than that of the first (for an explanation of this, see below). A second coat can be coloured with additions of other paints, although, if adding these in quantity, it would be best to avoid very slow drying pigments.

Gesso.

There are various recipes for making this, but the general procedure can be suggested as:

1. Prepare a small sample of size in the ratio 71/2- 8 parts water to one part size (i.e. about double the strength of sealant size) in the manner given in the section above. As with sealant size NEVER let it boil.
2. Test the strength of this sample, when allowed to cool, by pressing the resultant jelly with a finger. If it is of satisfactory strength the gel should split with ragged and not with smooth sides, which would indicate that the size is too strong and that the above ratio should be slightly adjusted.
3. Following the ratio which gives successful results, make up sufficient size for all the intended coats (i.e. at least 3).
4. Add the dry pigment. Nowadays the pigment mix which gives the best results would be, typically, 405g-450g of chalk or whiting, with 45g-50g of zinc oxide powder, which is added to increase whiteness and consistency, and which also prevents mould infection if you wish to store any surplus gesso left. These dry powders should first mixed together well, then should be gently stirred into somewhat under 2 pints of a still warm size solution. The resulting gesso should be creamily liquid in consistency; it should feel right to the user. Both the above ingredients should be available at good art stores.
5. Apply the coats of gesso in one session. There should be at least 3 coats, each applied as soon as, and not later than, the last is touch-dry (about 10-12 minutes). Take care not to allow the gesso to thicken up as subsequent layers go on; add a little warm water. Do not allow the gesso to dry on the brush; rinse it between coats. Do not trap bubbles in the applied coats; brush gently!
6. The resulting surface should be satisfactory if it is thicker than 1.5mm, and should be dry within 48 hours. It may still need a light abrading with sandpaper or carbide paper to smooth it out.
7. This surface, as it is, will also be too absorbent for oil paint, and so a weak sealant size solution (approx. 15 parts water to 1 part size) should be applied. Alternatively, to follow a17th century practice, a thin layer of linseed oil can brushed on to slake the surface, wiping off any excess later.

Acrylic.

Part of the attraction of acrylic primer is its straightforwardness. You simply have to apply it to the support, possibly slightly thinning the first layer with water according to the instructions on the can. But you should check out the brand of primer you intend to use by painting up a sample and coating this with some oil paint; some brands, particularly when applied in 2 layers or less, have a reputation for being too absorbent to serve as good oil grounds. Since acrylic primers should not be applied to a sized surface, they can also seem to make an unsized canvas feel rather slack and rubbery, lacking the spring of its sized counterpart.