I made my first wet palette yesterday. It's nothing fancy - a bit of washing up sponge and some baking paper in a pencil case. The whole thing cost less than three quid (including the pencil case and enough paper to last 40 years!)
Putting paint onto a wet palette keeps it workable for hours, not minutes - and all without any extender or retarder. So you use less paint because you're not replenishing what's just dried up every 15-20 minutes or so. During painting, you can snap the lid shut and go and have a cup of tea and come back and the paint is still good to use.
But it's even better than that.
Last night I was painting 'til the early hours (the wife is away and the nerds were all back home from playing at the local hackspace). I just snapped the paint lid shut and went to bed.
Eight hours later, I checked the paint as I walked past to put the kettle on. It was still fine!
Even after eight hours, the brush picked up the acrylic as if it had just come out of the bottle.
The wet palette kept may paint good for over eight hours! There's a little colour separation on the red and the blue paint, but that's nothing a quick mix around won't fix. Suddenly I'm able to use every drop of paint that comes out of the bottle. So now I'm no longer putting big blobs of paint down, in the vain attempt that it'll stay workable for 20 mins or more, in order to paint more than a couple of miniatures at a time.
For something so cheap and so simple, I was amazed at the results. The paints stay wet on the palette but - unlike using a retarding agent - they dry quickly on the model. Now I just need to improve my painting skills to get the best out of my paints!