Golden GAC Mediums
GACs can be blended with GOLDEN Acrylic Paints to extend the paint, regulate transparency, create glazes, increase gloss, reduce viscosity or improve adhesion and film integrity. The GAC polymers can also be used for binding pigment solids for various effects and surfaces. Unlike the other GOLDEN 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 very fluid, and thinner than other GOLDEN Mediums. Since they do not have thickeners added, these polymers will reduce the thickness of most GOLDEN Acrylic Paints. GOLDEN Fluid Acrylics are slightly thicker than the GACs, but will be the color line least changed in viscosity with any addition of a GAC polymer.
Each GAC product represents a unique polymer that offers certain specific attributes. Therefore, each GAC will have its own unique benefits and applications. Refer to the individual product description of each GAC (below) to find the proper medium to use for a particular application.
GAC 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 which will be very difficult to eliminate. Foam can severely affect the transparency of the film causing an apparent 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.
If spray application is desired, blend with GOLDEN Airbrush Medium. Start at 2 parts GAC Medium to 1 part GOLDEN Airbrush Medium. When faster drying is required, replace the Airbrush Medium with GOLDEN Airbrush Transparent Extender.
The GAC polymers are intended for use as binders, modifiers or additives for acrylic paints. They are not intended for use as a final varnish. Golden Artist Colors manufactures two different varnish systems, Polymer Varnish and Mineral Spirit Acrylic (MSA) Varnish (See the GOLDEN Varnish Information Sheets for more details).
Support Induced Discoloration:
Common supports (e.g. cotton canvas, linen, masonite) contain water-extractable materials that can cause discoloration in transparent glazes. To minimize Support Induced Discoloration (S.I.D.), prime support with 2 coats of GOLDEN GAC 100.
Replacing Rabbitskin Glue:
Traditionally, rabbitskin glue (also known as hide glue) was used to reduce the flexibility of canvas before painting. Although the rabbitskin glue does reduce flexibility, it is extremely brittle. It is hygroscopic, which means that it will always be water-soluble. Even when the glue is completely dry, high humidity will re-introduce water into the film, causing it to soften or swell up. Over time, this constant swelling and drying of the film can cause severe paint-film cracking and delamination.
GAC 400 can be used in a similar fashion for stiffening canvas. Apply directly to the front of the raw canvas 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 GAC 400 is not effective against oil penetration, the use of GAC 100 over GAC 400 is recommended for oil painters
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 cured oil paints.
Linseed Oil Blocker:
Two coats of GAC 100 before gessoing will substantially reduce linseed oil penetration into the canvas fibers. If stiffness and oil-blocking are desired, apply a coat of GAC 400 to the front, directly into the raw canvas, followed by one coat of GAC 100 onto the front of the canvas. Follow this by the desired number of gesso coats.
GAC 100: Universal Acrylic Polymer / S.I.D. Blocker / Most Flexible GAC Polymer
GAC 100 is a thin, translucent, gloss medium. Useful for thinning or extending colors as well as increasing flexibility. Wets out solids more readily than other polymers and is useful for creating homemade paints. GAC 100 provides basic protection from Support Induced Discoloration (SID), for better protection see GOLDEN Gloss Medium
- This polymer is one of the most universal used in paint manufacturing. Artists who had used "Rhoplex" (a registered trade name) will find that this GAC most closely reflects the properties to which they were accustomed.
- The GAC 100 is a useful polymer for protecting against Support Induced Discoloration (S.I.D.).
- The most flexible with a moderate level of tack and gloss.
- Useful for diluting and extending colors, especially when film flexibility and integrity are important characteristics.
- Wets pigment surfaces well. The most ideal for artists formulating their own paints.
GAC 200: Increases Film Hardness of Acrylic Paints / Increased Non-porous Surface Adhesion
GAC 200 Hard acrylic extender for non-porous surfaces is the hardest and least flexible polymer we offer. It is Ideal for mixing with acrylic colors to increase film hardness, reduce dry film tack and to increase adhesion to many non-porous surfaces. Dries to a clear, high gloss, finish. GAC 200 is not recommended for flexible supports.
- The hardest and least flexible of any Golden Acrylic product. Caution is advised when using this product alone.
- Used in its pure form, it is limited to applications on rigid supports, as its lack of flexibility may lead to cracking when flexed. Under certain conditions, the medium alone may crack upon drying.
- Ideal as an additive to acrylic paints to increase film hardness and reduce dry film tack.
- Improves adhesion to non-porous surfaces; however some surfaces, such as glass and glazed tile, will not allow for a permanent bond
- Dries with high gloss and excellent film clarity.
- Promotes cleaner edges of hard-edge techniques. The harder paint film has less "pull" as the masking tape is removed.
GAC 400: Fabric Stiffener / Rabbitskin Glue Alternative
GAC 400 Stiffens natural fibers and fabrics and is useful for stiffening unprimed canvas or sculpting and shaping fabric. Fibers saturated with GAC 400 will dry to a hard, stiff film.
- Dries to a very hard and stiff film.
- Most useful for priming fabrics (cotton, linen, silk, etc.) when stiffness is desired.
- Used as a rabbitskin glue alternative when applied directly to raw canvas or linen.
- Allows sculpting and shaping of draped fabrics.
- Note: Optional heat setting will decrease water sensitivity but also releases low levels of formaldehyde; therefore if choosing to heat set it is recommended that adequate ventilation be provided.
GAC 500: Self Leveling Applications / Hard Yet Flexible / Best Isolation Coat Medium for Spray-Application
GAC 500 Gloss extender for Fluid Acrylic Colors is a unique balance of film hard