Re: How to soften gouache?
Irene, I find that once they dry, it's almost impossible, if at all, to get that consistency back. Like Carol, I tend to use the dried paint for the more transparent parts of a painting, or for light washes over existing color. If the glob on the palette is big enough, try dropping a couple of drops of water on it, then take a stiff wet brush and work it into the glob. Sometimes I manage to squeeze some solid paint out that way.
Generally, though, I've just learned not to put too much paint out at a time. It means I'm constantly mixing again to get the same color, which can be trying at times, but I tend to work very opaquely most of the time, and use a lot of paint, so I really hate to waste it.
I also squeeze the paint out on a folded strip of wet paper towel, and spray the towel frequently. And my palette is an aluminum pan with a plastic lid that I buy at the grocery store. Spraying one last time before you stop, then putting the lid on the pan, will help keep the paint soft overnight.
Hope this helps.