I'm trying to keep my watercolors soft so I can transfer them to a new porcelain pallet, so I wet them really well, then packaged tham up using plastic bags. I haven't been painting for a couple weeks because I wanted them to soften. I looked at thm yesterday, and some of them had mold on top. I took it off, cleaned it up. I have to keep them soft until July 23.[my birthday] What can I do?