Re: How do I treat Acrylic Gouache?
I would echo that the Turner Acryl is essentially a matte acrylic paint; however, it is different than regular acrylic that has a matte medium added to it. The weaker binder dries more slowly than regular acrylic, and after about an hour or so you can scrub it down with a damp rag, whereas a thin acrylic paint wouldn't budge. You can add an acrylic retarder to slow the drying even more. Also, because it's acrylic, you can work on stretched canvas, which is not recommended with traditional gouache. Another nice thing is it comes in large sizes, up to 500ml bottles.
One feature it has for use with traditional gouache is that you can use it for underpainting once it dries, even getting fairly opaque, without the gouache paint picking up the paint underneath. You can mix them together; although, the more acrylic it has, the more like acrylic it will behave.
The one negative I have about Turner, including their traditional gouache, is that their paints are sometimes very strange mixes. For example, their burnt umber is a mix of several pigments (red oxide, magnesium, and black) unlike most other companies that just use Pbr7. It looks similar, but will behave differently mixed with other pigments. They also like to use some non-descriptive names like "apricot." Check their pigment labeling to be sure you're getting what you expect.