I wanted to make a polymer clay coaster, but friends told me that unprotected clay would be stained by coffee, tea, soda, etc. Suggestions were made to seal it with resin or varnish, which meant testing. Please note that polymer clay is not deemed safe to use for serving food.
First, I looked up which foods created the worst stains. I decided to test the following: cranberry juice, chocolate syrup, coconut oil, mustard, ketchup, black tea and coffee. When I was ready to test, I made strong brews of tea and coffee.
I cured sheets of six brands of polymer clay: Premo, Cernit #1, Pardo Jewellery Clay, Soufflé, Fimo Pro and Kato.
I cured several more sheets of Premo and covered them with EnviroTex resin, Translucent Liquid Sculpey, Genesis Heat-Set Satin Varnish, Kato Liquid Polyclay, Fimo Liquid Gel, Cernit Matte Varnish, Final Coat, Varathane Gloss and Fimo Gloss Varnish. After the initial testing, I decided to test Renaissance Wax, too.
My choice of sealers was based upon previous testing of those that didn’t scratch off. Varathane, Final Coat and Renaissance Wax didn’t meet this criteria, but I tested them anyway.
Some of the sealers blurred my handwritten notes on the clay.
I applied two coats of the varnishes with a day to dry in-between. Then I allowed another three days to dry after the second coat. I applied only one thick coat of the liquid clays, resin and heat-set varnish.
Below are the test sheets with food applied.
The top row, left to right is: cranberry juice, chocolate syrup, coconut oil and mustard. The bottom row, left to right is: ketchup, black tea and coffee with grounds. Some didn’t want to stay where they were put. In spite of my efforts, those on the Genesis Heat-Set Varnish flowed together because the varnish had caused the sheet of polymer to cup.
After 24 hours, the food was all dry. The cranberry juice and chocolate syrup still looked wet, but they just dried shiny. You can see the coffee grounds left in the coffee.
Then, I washed them all off. I scrubbed with warm water, mild dish soap, a plastic scrubby and I even had to use my fingernail to scrape off the mustard and ketchup.
In the process, the Final Coat got a few small scratches and the Varathane came off in pieces as shown in the photo below. Cernit Matte Varnish and Fimo Gloss Varnish didn’t scratch off at all. These were all applied to cured Premo polymer clay.
The overall results are below:
Of the plain, cured polymer clays, all were stained by food, though Pardo was the least affected. All of the liquid clays stained, too.
The resin did very well. There was a small bare spot which mustard seeped through. Other than that, it was unstained.
Fimo Gloss Varnish did fairly well, but wasn’t a total success.
Coffee stained more than tea, but with repeated use, stains would build up. The mustard stain was like yellow neon, probably caused by the turmeric. Ketchup made a fairly strong stain, too.
I thought maybe Pardo did well because it contains beeswax. This led me to test Renaissance Wax. I applied a coat of wax, let it dry, buffed it with a cotton cloth and repeated the process to add a second coat.
I don’t always like the extreme shine of resin, so I dulled it with fine steel wool.
I tested both with just the worst offenders: ketchup and mustard.
By roughing up the surface of the resin with steel wool, I made it susceptible to staining. The mustard stain was faint and it did resist the ketchup. Renaissance Wax didn’t work very well.
Of the products tested, resin seems to be the only way to really protect the surface of polymer clay from food stains. Pardo Jewellery Clay was the most stain resistant of the polymer clays. Fimo Gloss Varnish worked fairly well, but wasn’t totally successful.
UPDATE: I tried 3M Scotchgard Clear Paint Protection Film and it didn’t repel food stains either, plus it has kind of a bumpy finish.