Yesterday we experienced some rapid drying conditions while we were trying to paint multi-layer skies. The edges of the clouds were hard before we could even get two layers applied, making the shapes look more like baked potatoes than soft clouds. What can we do to keep the paper wet as long as possible? Is there anything we should do if hard edges appear before we're ready?
Let's look at the second question first. If you see hard edges where you intended soft ones, stop painting! It does no good to keep making hard edged marks. Instead, let the painting dry thoroughly and re-wet the area where you want soft edges. Then carry on making the soft clouds. Re-wetting is a powerful tool that takes away the feeling of panic. Just remember the paper must be all the way dry before you lay on a new layer of water. A little practice reveals the techniques and puts you back in charge.
Now, back to the question of prolonging the drying time. More water seems to be the obvious solution, right? What if you wet both sides of the paper? Or let the sheet of paper sit in the sink for a few minutes. You'll probably need to use somewhat thicker paint for the second layer to keep it from feathering too far.
Here are a few paintings and photos to guide your experiments. Try counting how many layers it would take to paint them.