I paint a lot of metal minis, which has led to a small scale obsession with strong primers. The dream of a non-toxic brush on primer that can adhere to metal like a spray enamel keeps me curious. I'm a fan of Golden products, so when I heard about GAC 200 I had to pick it up from my local art store and give it a try.
WHAT IT IS"GAC" = Golden Artist Colors. "200" = a mysterious number they assign to their specialty mediums. As the bottle says, it's a hard acrylic medium for non-porous surfaces. It thins with water, and can be mixed with any acylic paint. Golden even says that it can be used undiluted to prep glass for acrylic paint. Sounds perfect for adhering to white metal!
HOW TO USE ITThe instructions say to mix it with an acrylic paint, up to 3:1 for rigid surfaces, up to 2:1 for more flexible ones. Though I expect for our purposes we're going to have to do some science to find the right mixture.
THE FIRST TESTIn this initial experiment I have painted the top of a plastic gesso jar. The interior colors are a 4:2:1 mix of paint/GAC/water, and the black is a 3:1 mix of GAC/paint. The first thing to note is GAC 200 takes a while to fully cure. I tested the strength of the paint film with the very scientific "fingernail scraping test" after it was dry to the touch, and then again the next day. The chips and scrapes you see in the photo are almost all from the first day. It was much more difficult to scrape day 2. The black, which was the higher ratio of GAC to paint, was expectedly much stronger than the other colors.
Another thing to be aware of is that this is a high gloss medium. In 1:1 ratios or greater even matte paint becomes pretty glossy. 2:1 ratios appear satin.
PRACTICAL MINIATURES TESTThis model was painted with a 2:1 ratio of Vallejo matte black to GAC 200. For whatever reason I didn't add any water to this one and it has some brushstrokes showing. It takes 2 or 3 thin coats to get a nice opaque coverage, nothing out of the ordinary there. After letting it cure the paint film stood up well to a fingernail test. A strong satin finish. Not bad.
I have also heard of people tinting glass & tile mediums with acrylic paint as a primer. I decided I would also try something like this. This model has a 2:1:1 mix of GAC/paint/flow improver. It leveled nicely, is glossy and strong, but this mixture has a bit too much paint and came out too dark for me. I would probably not use this one, it seems like splotchy wash means more work in the painting process.
Here's a finished model that was primed using the first mixture, 2:1 paint/GAC with a little water. The smooth finish wasn't a major impediment to painting, but it certainly wasn't as nice a as the fine-toothed surface that a dusting of auto primer gives. The gloss was ok as well, but with a higher ratio of GAC to paint it would probably be desirable to matte varnish right after priming.
SO WHY WOULD YOU DO THIS?Well, there are a few things going for the GAC: It's strong, can be brushed or airbrushed on indoors, doesn't have any fumes, and any color in your paint collection can become primer. Downsides are that is is very glossy, takes longer, and you have to figure out the custom ratio of paint/medium/thinner that is right for you.
Personally I don't see this replacing my spray primer, but for the odd tabletop mini that wants a custom primer color this might be a nice option. I could also see an application for this in painting terrain which gets knocked around a lot, and might benefit from a more durable finish.