Breaking it Down Further... Gels & Mediums
There are a few general distinctions that once remembered make the whole group of gels and mediums seem much less difficult to understand.

The main property that differentiates a majority of products is viscosity - that is, how thick or thin a product is. This is what actually separates the gels from the mediums. The mediums are the thinner products, while the gels are thicker, having higher viscosities. The mediums are thin enough to be pourable, while the gels are not.

Within the gel grouping, the names reflect the scale of viscosity, and not any differences in feel of dry films. Soft Gels are thinner than Regular Gels, which are thinner than Heavy Gels, which in turn are thinner than Extra-Heavy Gels. Heavy Gels do not weigh more, and Soft Gels do not feel spongier or more flexible when dry.

The second key property is reflectance or sheen. This is the most important difference between Polymer Medium Gloss and Matte Medium. In the gels, nearly all are available in Gloss, Semi-Gloss and Matte finishes. Hence, a Heavy Gel Gloss and Heavy Gel Matte will feel very similar in consistency, but will dry with different sheens. The Semi-Gloss gels dry to yield a similar appearance as wax, and this aspect has been used extensively to create wax-like impressions.

Then there are the specialty products that do not fit into the above differentiations. These products have a unique property requiring a different naming convention. In such cases, Golden has tried to assign a name that has significance to the products most unique feature. For instance: High Solid Gels have higher levels of polymer solids than the other gels (approximately 60%, versus 45-50%); Light Molding Paste allows for thick film build without being correspondingly heavy in weight; Pumice Gels are composed of pumice (volcanic lava) and are ideal for creating rough, granular surfaces; etc.

Summing it up:

Learning the Rules
As implied from the all of the previous information, there is not a lot of limitation or restriction on the use of gels and mediums. An artist can mix any quantity of Gel with Golden Acrylic colors, or other Gels and Mediums. However, the following are rules that should be obeyed:

* To thin, add a thinner Golden Medium or water.
* When blending thin products into a gel, add in small portions with thorough and careful stirring at each addition.
* For slower drying, add Golden Retarder, but do not exceed 15%, as it will result in a surface that will not lose its tack. Acrylic Glazing Liquid can be used in place of straight Retarder, and there are no restrictions on amounts.
* Do not mix with oils.
* Abrade non-absorbent surfaces for increased adhesion.
* Minimum film formation temperature is 49oF/9oC. Avoid freezing.
* Paint on any non-oily surface.
* Clean tools and brushes with soap and water.

Controlling Foam
Be aware that nearly all acrylics have a propensity to foam and get air trapped within them. This can be most dramatic when applying glazes and various translucent effects. Therefore, it is important to take proper precautions and to handle the materials carefully. This includes: avoid shaking, do not whip or stir excessively, refrain from generating a vortex during mechanical mixing and pour and handle slowly and carefully. Refer to the article in Just Paint Issue # 4, entitled "Taming the Foam Monster in Acrylic Paint," for more complete information on foam.

Drying Acrylic Films
Drying times are influenced by many factors. The most important factors are the thickness of application and the temperature, humidity and air flow conditions in the working area. While acrylics surface dry, or skin over, very quickly (sometimes within minutes), they typically take much longer, sometimes months, to thoroughly dry. Obviously, the thicker the film, the slower it is to dry. The development of clarity in the film does not occur until the gel or medium is fairly dry. A 1/4 inch thick film of a Gloss Gel will take a week or two, even in ideal conditions (70-80oF, relative humidity of 50% or less and a moderate flow of air in drying area) to develop clarity. When humidity pushes over 80%, that same Gloss Gel may remain cloudy for several months. (For more information on drying considerations, refer to Golden Information Sheet: "Technical Notes on Drying").

Stopping Support Induced Discoloration (SID)
Common supports (e.g. cotton canvas, linen, masonite) contain water-extractable materials that can cause discoloration in transparent glazes. This manifests itself as a yellow or brown tone, and is especially of concern when the glazes are thickly applied (greater than 1/16 inch wet film thickness). To minimize Support Induced Discoloration (SID), seal support with Golden GAC 100 or GAC 700, followed by gesso. Note that multiple coats of gesso alone will not be sufficient to protect from SID.

True Varnishes vs. Acrylic Gels and Mediums
One final point to make about the use of gels and mediums is that all of these products are NOT recommended as final picture varnishes. Generally speaking, these products do not have proper balance of properties for such application. They are all either too soft, too hard, or they simply foam up too much to be a clear topcoat. They also all lack the property of removability. None of the gels or mediums are removable in a manner that would not harm the underlying paint films, and this is an important consideration for final varnishes.

Soft Gel Gloss, thinned 2:1 with water, on the other hand, is recommended as an "isolation coat". An isolation coat has several functions. Applied after completion of an acrylic painting, it seals the surface, lowers the absorbency of the surface, allows for a more uniform varnish application and serves to protect the acrylic paint during varnish removal. Not applying this coat can cause serious side effects, such as the varnish absorbing into a porous support. For spray application of an isolation coat, a mixture of GAC 500 (2:1) with Airbrush Transparent Extender is well suited.

More Information... Individual Medium Descriptions:

Polymer Medium (Gloss)
A general purpose liquid medium useful for creating glazes, extending colors, enhancing gloss and translucency and increasing film integrity. Its unique feel is oil-like or resinous in nature, and promotes flow and leveling.

Fluid Matte Medium
A liquid medium useful for extending colors, decreasing gloss and increasing film integrity. Useful for blending with Golden Fluid Acrylics to decrease the gloss without increasing viscosity.

Matte Medium
A general purpose, pourable medium useful for extending colors, decreasing gloss and increasing film integrity. Can be used as a ground instead of gesso.

Super-Loaded Matte Medium
Same consistency as the regular Matte Medium, but with three times more matting solids. Excellent for lowering sheen of glossy paints and other mediums (the least addition of medium is required). Slightly increases opacity.

Airbrush Medium
Modifies the Golden Fluid Acrylics for airbrush/spray application. Blends easily with the Fluid Acrylics to yield a paint mixture with the proper viscosity for airbrushing. Effectively decreases clogging and tip buildup during spraying, eliminating the largest drawback to airbrushing with acrylics. While designed with the Fluid Acrylics in mind, Airbrush Medium will also reduce the Heavy Body, Matte, High Load, Iridescent/Interference and Fluorescent Acrylics and Golden Mediums and Gessos for spray applications.

Airbrush Transparent Extender
Essentially a "colorless airbrush color". Designed for extending Golden Airbrush Colors to increase film hardness for better frisketing, and to lower the pigmentation of the colors. This allows an artist to achieve a transparent paint without sacrificing spraying properties. Also useful as a topcoat for frisketing on softer acrylics. Blend with GAC 500 (2:1) to Airbrush Transparent Extender for a sprayable isolation coat before varnishing. While designed with the Airbrush Colors in mind, Airbrush Transparent Extender will also reduce the Fluids, Heavy Body, Matte, High Load, Iridescent/Interference and Fluorescent Acrylics for spray applications.

Silk-Screen Medium
A water-borne system designed to blend with acrylic paints for silk-screen application. Increases working time and retards paint from drying in the screen. Safe to use with minimal odor. Mix 1 part Silk-Screen Medium with 1 part Golden Acrylic colors (Heavy Body, Matte or Fluid) and use this mixture to screen with. The Silk-Screen Medium is not designed to impart opacity, hence the opacity of the mixture will be determined by the nature of color being used and the ratio of paint to Medium used.

GAC Specialty Polymer Acrylic Mediums

GAC-100 Acrylic
A liquid acrylic polymer emulsion useful for diluting and extending colors as well as increasing flexibility and film integrity. Wets out solids more readily than other polymers and is useful for creating homemade paints. The best Support Induced Discoloration-blocker we make.

GAC-200 Acrylic
A liquid acrylic polymer emulsion that is the hardest and least flexible of Golden acrylics. Useful for increasing film hardness and reducing tack. Improves adhesion to non-porous surfaces; however some surfaces, such as glass and glazed tile, will not allow for a permanent bond. Used in its pure form, it is limited to applications on non-flexible supports. Generally recommend a maximum level of GAC-200 be 75% of the entire paint mixture. Great for increasing durability of Golden Acrylic Paints for mural use.

GAC-400 Acrylic
A liquid acrylic polymer emulsion which dries to a hard, stiff film. When applied over a fabric support, such as cotton, linen or silk, the GAC 400 will serve to dramatically stiffen the support. This allows the artist to transform a lightweight fabric into a free-standing form that will hold its shape.

GAC-500 Acrylic
A liquid acrylic polymer emulsion with leveling ability, that forms a hard, glossy film. Useful for increasing film hardness and reducing tack, while maintaining flexibility. The hardest polymer that is suitable for flexible supports.

GAC-700 Acrylic
A liquid acrylic polymer emulsion that offers excellent film clarity and gloss. Excellent for sealing various supports to protect against Support Induced Discoloration. Useful for glaze applications, but care needs to be exercised to avoid foaming. Offers reduced shrinkage.

GAC-800 Acrylic
A liquid acrylic polymer emulsion that does not craze in pours/puddles. That is to say that it dries with the same uniform surface and dimensional integrity as when wet (other GACs will craze, developing shrinkage crevices running across the surface). Dries with good gloss and flexibility, but only moderate clarity. Useful to increase adhesion to chalky surfaces.

GAC-900 Acrylic
A liquid acrylic polymer emulsion which when heat-set offers a very soft hand and laundering stability. This product is most useful to artists painting on clothing. GAC 900 can be blended with various acrylic colors to produce fabric paints that can be airbrush, hand brush or screen applied.

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