Crackle varnishes are available either in oil-based or water-based varnishes. Oil-based crackle varnishes are generally completely transparent and provide an authentic craquelure effect, but are difficult to find and to use. Water-based crackle glazes are available as transparent or opaque colored glazes. Oil-based crackle varnishes should not be used on walls, but can be used on wood and canvas.
When buying supplies for craquelure, you will often have the opportunity to buy the crackle varnish along with a special antiquing varnish that has a yellowish tinge. When using oil-based craquelure, antiquing varnish should be applied first, in an even layer with a stiff varnishing brush. After about an hour, apply the crackle varnish and let it dry for about 45 minutes. If cracks do not appear by this time, a hairdryer should be used on a low setting, producing a pattern of fine cracks.
In very cold or extremely humid weather, crackle varnishes sometimes fail to crack. If this happens, clean the surface off with water and begin again. Otherwise, let both layers dry and reapply both the antiquing varnish and crackle varnish. If the second approach is taken, the craquelure may even have secondary cracks which appear under the first layer.
Water-based crackle varnish is performed in essentially the same way as oil-based crackle varnishes, but with much shorter drying and cracking times. Water-based crackle varnish often creates a craquelure effect which is in a very regular pattern, not always looking realistic.
Crackle varnishes are colorless, adding depth and texture, but not color. This can be changed by tinting the glaze. If tinting craquelure, use a wash of one part artist's oil pigment and four parts paint thinner. After the cracks appear, wipe the tint on with a clean rag and wipe off with a different rag, leaving color in the cracks.
Crackle glaze can be used in lieu of crackle varnish, for an opaque effect. Opaque crackle glaze is water-based and is applied between two layers of water-based paint. This causes the top coat of paint to crack and expose the color underneath. Crackle glazes should not be applied over a design, but only over solid colors.