GAMBLIN GUIDELINE IN BUILDING PERMANENT PANTINGS
In painting there are no "rules," only techniques and guidelines. Generations of oil painters, however, have demonstrated how to build permanent paintings.
*Overall Gamblin Painting Guidelines: A painting made with a simple structure will last longer.
*If painting vision calls for multiple layers and mixed mediums, follow your vision and understand what you are doing. Try not to complicate the structure unnecessarily.
Foundation
Support: When choosing a fabric, choose the fabric you like to paint on. Linen is the best choice if painters like the best. From a conservation viewpoint, regardless of the fabric support (linen or canvas), painting are relined at 100 years. Choose good quality fabric with warp and weft made of the same materials and weight. For example, a fabric made of cotton warp and a Dacron weft would not be good choice. Fabric should not be treated with any chemicals like waterproofing that may interfere with adhesion.
Birch ply panel, free of chemicals, glue or grease, is a good rigid support. If using more than 30% beeswax or beeswax medium to 70% oil colors, consider painting or rigid supports or paintings may crack when moved. The back of the panel should be braced to prevent warping.
To prepare a fabric support for oil painting: Robert Gamblin recommends PVA Size to seal the Fabric. Rabbit skin glue is "hygroscopic" - that means it is constantly swelling or shrinking in response to changes in temperature and humidity. The movement of the glue size cause the oil paint on top of it to crack over time. PVA sizes is not hygroscopic PVA does not tighten the fabric like rabbit skin glue, so stretch fabric tightly. The size protects the fabric from the ground.
Ground: Gamblin Ground is a non-absorbent ground like a traditional oil ground. Paintings made on non-absorbent grounds are brighter because the oil is left in the paint film rather than absorbed into the ground. Two thin layer of Gamblin Ground equal four layers of acrylic gesso. Instead of linseed oil, Gamblin Ground is made with alkyd resin because of its increased flexibility and quicker dry time. Traditional linseed oil ground need about six months to dry before painting on them. Gamblin Ground is ready for paint application in a few days. Oil grounds may be used directly upon panels without sizing.
Gamblin Gesso, an absorbent ground, is a traditional dry gesso which is mixed with water and applied only to panels. Painting on gesso (either traditional or acrylic) are more matte because of the high absorbency.
If you prefer acrylic gesso, use only the best acrylic gesso that has been formulated for artists' use. Beware of cheap gesso, which can be just re-labeled commercial house paints. Use three to five coats, lightly sand the final coat. Do not thin acrylic gesso with water. Acrylic paints are not the same as acrylic gesso. We do not recommend under painting acrylic paints. There is a reason to believe that over time, the oil paints will not adhere to acrylic paints.
Paint Layers
Observe the "fat over lean" guideline - do not put a lean color, such as Cadmium, over a color with a high fat content, such as Ivory Black. Cracking will occur as the fat layers starts to dry, swells, then crack s the lean layer to dry completely. When using a high proportion of white, consider the layer lean. For under paining layers, thin paints with a mixture of medium and solvent rather than only solvent.
Preferably, use one medium per painting. Consider the medium as a crucial element in painting the "fat over lean" guideline. In the under layers, thin medium with solvent in the proportion 1 part medium to 1 part solvent. The middle layers, use 2 parts medium to 1 part solvent. In the upper layers, use medium only. Gamblin Galkyd Mediums increase the flexibility of oil painting in speed the drying time. Galkyds do not yellow or darken with age like natural resin mediums. Cold Wax Mediums can be used to make oil painting materials more matte.
Using Cold Wax Medium
Using Gamblin Medium
Varnish
Varnishing is an aesthetic decision. A varnish layer will change how a painting looks. It will unify the surface and saturate the colors.
Gamblin Gamvar looks as good as damar but never yellows or crosslinks. Gamvar is easy to remove with mild solvents.
Gamblin Cold Wax Medium can be used as a traditional wax varnish.
A light coat of wax can be applied over a dried painting then buff with soft, line free cloth. A wax varnish gives a painting a soft sheen without the thick resin coating. Gamblin Cold Wax Medium can be applied as vanish any time. Conservators recommend waiting six months to apply all other varnishes.
If you would like to unify the surface and saturate the colors without varnishing, consider a clear glaze layer of Galkyd or Galkyd Lite thinned with 50% odorless mineral spirits.