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Technical Forum: Your Acrylic Materials questions meet technical expertise

The dialogue continues. Here are some topics covered in Golden Artist Colors ongoing technical support program. We hope you find the information useful, and remember, when acrylic quandaries arise we are available and interested.

Settling and separation due to accelerated testing

I use GOLDEN Fluid Acrylics and like to mix custom colors that I use often and store in my empty Fluid Acrylic bottles. Does mixing the paint diminish the shelf life of the paint in any way? (I don’t add any mediums or additives to the paint).

Most paint mixtures should keep well on the shelf. However, the earliest sign of a negative change is to notice the mixture thickening. This doesn’t necessarily mean the paint is unusable, but it’s an indication to try to use up the paint fairly soon.

Also, some colors simply have better shelf stability than others do. Whites, Blacks, Phthalos, Pyrroles, Hansas all come to mind for great long-term fluid stability. Some Quinacridones, like Magenta and Red, do much better than Quinacridone Gold and Violet. Earth colors commonly thicken up faster than other colors.

As you can see, this variation of pigment keeps us very busy in the lab, and we are constantly trying to improve shelf life. Our goal for each product is about ten years or more of shelf life when stored in normal room environments.

Blending colors does add another dimension to all of this; however, as long as the containers are sealed and kept well, they should remain usable for many years.

I have applied an isolation coat to an acrylic painting using GOLDEN Soft Gel Semi-gloss. This time it didn’t dry clear (possibly not thinned enough and/or over-brushed?) and has retained a milky white appearance in some areas. Is this material indeed non-removable, or is there something I can do short of painting over these areas?

First of all, you should be using the Soft Gel Gloss instead of Semi-gloss, as it has much better clarity. This may be part of the cloudiness you are seeing. An isolation coat is: one or more acrylic medium layers applied after the artwork is complete. A gloss product is going to have much better overall clarity and regardless of the desired final sheen, if applied correctly, it can be undetectable to the viewer.

"Threaded Rod" applied Carbon Black with isolation coat
brushed to assess texture-generated foam

Secondly, sometimes the final clarity can take a while to develop depending on the temperature and humidity conditions of the studio, so you may wish to observe the work for another day or two to make sure the Soft Gel Semi-gloss layer is completely cured.

Finally, if you didn’t mix at least a 2:1 gel to water ratio, the gel is much more susceptible to holding foam when brushed out, especially if the gel is overworked or applied over a textural surface. The added water allows the foam bubbles to rise and pop instead of being trapped in the film.

You’re correct with your thoughts about the permanency. Regretfully, there is nothing you can apply to remove only the isolation coat that will not alter the underlying artwork. Depending on the nature of the piece, you may be able to carefully sand down through the Soft Gel, but beyond that, painting over may be much easier and faster. I’m sure this is not the news you wanted to hear, but this is an invaluable lesson to learn so that you do not repeat the effect unless desired.

Can you clarify how GOLDEN’s GAC 200 is best used in hard-edged painting?

The best use of GAC 200 - a hard, low-tack acrylic medium - for hard-edge painting is to blend it with acrylic paints and mediums. By adding this product to the regular paints and other acrylic products, you reduce the stretchy, elastic nature of a fresh acrylic film and this in turn means your hard edges will be cleaner.

Even a 15% addition of GAC 200 into a paint mixture will begin to lower the elasticity. It is also useful to blend with another medium, like Polymer Medium Gloss or GAC 100, and paint this over the inseam of a taped line. The medium will seek any crevices and fill them. When the intended paint films are applied over the dried medium, it cannot seep under the tape and when the tape is removed the paint line will be smooth.

Ratios will depend on how much trouble you are currently having with achieving hard edge lines. A studio’s environmental conditions change daily. If you have problems that seem to crop up for no apparent reason in a technique you commonly do, take note of temperature and humidity in the area where you work. Certain colors and products can be softer than others as well, so keep this in mind while working. It will require some experimentation, but in the end, you should notice an improved line.

I tried to “marble” (create intricate patterns by floating color onto a bath of thickened water) with GOLDEN Fluid Acrylics, but most colors just sank down into the medium. What am I doing wrong? Can
I use the Fluid Acrylics for Marbling?

Most GOLDEN paints - including GOLDEN Fluid Acrylics - can be used for marbling. The key to marbling is controlling the surface tension between the bath and the paints. First, correctly prepare the bath by carefully following the supplier’s directions. Methylcellulose and Carageenan are the preferred thickeners used by most professional marblers. Once mixed, the bath should sit for a couple of hours to make sure it is uniform and free of air bubbles. Fresh bath is critical because once it starts to become contaminated with paint, the surface tension is equalized between the paint and the bath and thus the paint cannot remain suspended on the surface.

Fluid Acrylics are generally too thick to use straight from the bottle, and will need to be thinned with water. It is important not to over-thin the paints if you want strong color, and it’s important to “balance” the colors before beginning to attempt creating patterns. Each color will behave differently at any given time, and this is something that each marbler comes to realize and anticipate each time they marble.

Since each color is unique, some paints will automatically work fine, and others will be more stubborn. The more stubborn colors will need to be modified with GOLDEN Acrylic Flow Release (AFR). AFR is a surfactant: its job is to reduce surface tension in the paint to allow it to flow. The bath has a high surface tension so the colors don’t want to sink into it. This is the key to balancing the colors. We do put some surfactants into the paints already, but sometimes it’s not enough to allow heavier pigments to stay suspended. That’s why each color needs to be tested and mixed individually. If too much AFR is added, another problem will occur. That color will be a fast spreading mix, and it will force the other colors to sink.

Using an eyedropper or pipette, place one drop of each color onto fresh bath and examine how it spreads. Note the rate of spread and size of the spread circle and try to adjust each color to create a similar look. Once the colors are fairly balanced, then the focus becomes one of sequence. Some colors, usually the faster spreading colors, are good to apply first, and then slower spreading colors can be applied and so forth. This is something that will become apparent the more marbling one does, so be patient and do plenty of experimenting.

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