GAC 200 is a liquid acrylic polymer that promotes adhesion and film hardness and is the hardest and least flexible polymer made by Golden Artists Colors. It increases film hardness, reduces dry film tack and increases adhesion to many non-porous surfaces. Dries to a clear, high gloss, finish.
GAC (short for Golden Artist Colors) Specialty Acrylic Polymers are based on 100% acrylic polymer emulsions. The GACs are useful as mediums or modifiers of acrylic paints. GACs can be used to extend acrylic colors, to regulate transparency, create glazes, increase gloss, reduce viscosity or improve adhesion and film integrity. GAC polymers can also be used for binding pigment solids for various effects and surfaces. Unlike the other acrylic mediums and gels, GAC Acrylic Polymers have only a minimum amount of thickeners, levelers, defoamers and surfactants to ensure good film formation.
The consistency of the GAC polymers is more fluid and thin than other acrylic mediums, so they will reduce the thickness of most acrylic paints. Each GAC is a unique polymer with unique benefits and applications. Refer to the product descriptions below to find the proper medium for a particular applications.Replacing Rabbit Skin Glue
Traditionally, rabbit skin glue (also known as hide glue) was used to reduce the flexibility of canvas before painting. Although rabbit skin glue does reduce flexibility, it is brittle. It is also hygroscopic, which means that it attracts moisture from the environment and tends to remain water-soluble. Even when the glue is completely dry, high humidity will re-introduce water into the glue, causing it to soften or swell up. Over time, this constant swelling and drying of the film can cause paint-film cracking and delamination.
GAC 400 can be used in a similar fashion as rabbit skin glue to stiffen canvas. Although the GAC 400 will not quite achieve the stiffness of the rabbit skin glue, it does not remain water-soluble. Apply one or two coats directly onto the raw canvas, coating both front and back for maximum stiffness. It is imperative that it be applied directly to the raw canvas. It is ineffective over any other medium, and most likely will flake off and cause delamination of subsequent paint layers. Since it is an acrylic polymer, it is not hygroscopic. However, neither rabbit skin glue nor GAC 400 is completely effective against oil penetration, however two coats of GAC 100 will substantially reduce oil penetration.
Note: Since GAC 400 is brittle, it is important that it not be rolled tightly or bent back upon itself. This will cause cracking of the polymer film and may transfer cracks into additional paint layers. This is especially a risk with hardened oil paints.Linseed Oil Blocker
Two coats of GAC 200 before priming will substantially reduce linseed oil penetration into the canvas fibers. If stiffness and oil-blocking are desired, apply a coat of GAC 400 to both the front and back, directly into the raw canvas, followed by one coat of GAC 200 onto the front of the canvas. Follow this by the desired number of primer coats.Mixing
Golden Artists Colors (GAC) acrylic polymers should be gently stirred or rocked back and forth prior to use, but should never be shaken, as this will incorporate significant amounts of foam that will be very difficult to eliminate. Foam can severely affect the transparency of the film causing a foggy or hazy quality. When applying with a brush, use minimal agitation and force, and do not overwork, as this too will result in foaming.Drying Considerations
GAC acrylic polymers are milky-white and relatively opaque while in the wet state, but when completely dry they will become transparent/translucent (depending on the nature of the specific GAC).
The amount of time that an acrylic takes to dry completely is dependent on several variables, including film thickness, ambient temperature and humidity, air flow patterns and the absorbency of the support. A relatively thin film (approx. 1/16 inch) may take from 10 hours to 4 days to lose the milky quality, while a film 1/4 inch thick may take 2 to 10 days or more. It is important to note that film clarity occurs before the film has completely dried, or cured. The thin film mentioned above will take 2 to 3 weeks to achieve complete dryness, while the 1/4 inch thick film will take 2 to 4 months. This is very important to consider when determining how artwork is to be stored. When film transparency is critical, artwork should never be stacked or subjected to high humidity conditions.