I would paint with oils if I could find the materials I want, but I can't so I'm left to make due with acrylic paints and we all know how fast they can dry. So for all those of you who like acrylics for one reason or another but can't stand your palette turning into solid chunks of paint in 5 minutes, here are some possible solutions.
Keeping the paints wet requires keeping them well... wet, and that can be achieved either through physical or chemical means.
I already made an instructable on making small containers to store small mixes for a very long time. The containers are made from bottle caps which are easy to get. So check that out. This instructable will focus more on keeping the paints wet while mixing. The bottle caps work nicely for keeping your main colors wet, but not so much for those temporary mixes.
I won't be going over everything in the videos, just giving a brief overview and some additional info.
This first video covers retarders, the different types, and how to make your own from Propylene Glycol, medium, and water (preferably distilled), and some useful recipes. As I explain in the video, I would avoid Glycerin, which is often recommended, as it tends not to leave the paint film. Propylene Glycol has a much higher vapor pressure point and as you can see from my tests which where done in the winter (when water wants to evaporate even less) even in large quantities (which you wouldn't reach) it still dries within the week. I could not get a similar sample of glycerin to dry unless I left it for several days over the extreme heat of my heater.
Here is drying test chart on google drive if the image is too small. Not the most scientific test but useful. Summer tests coming in a few months.
Step 1: How Much Can You Dilute Acrylic Paints?
When using retarders and mixing them in directly with paints, just as with water, there are limits to how much you can mix in without the paint becoming too fragile, but I have personally found that limit is much higher, at least for professional grade paint, than the 50% water to medium commonly stated (which would mean even less for paints straight out of tube). Still you should conduct an adhesion test for your specific brand if you like to dilute your paints a lot. This second video shows you how to do that and how you might be able to protect paintings where you diluted the paint too much.
If you are using paper there are no limits because paper is absorbent and you can actually make a sort of acrylic watercolor substitute by mixing in a lot of retarder as I show in my first video.
Step 2: Stay Wet Palettes and Silicon Palettes
Stay Wet Palettes
But then if you don't like how your paint behaves when using retarders, how much they might need to be diluted if it's really hot, or maybe you actually want the paint to dry fast on the canvas, the. You can use a stay wet palette. In the video I show you how to make one, specifically what paper to use as it might be hard to find in countries where wax and parchment paper are called the same thing. We want parchment paper, an opaque paper, similar to tracing paper, that's made by being coated in a thin layer of silicone, and can withstand a lot of heat. It should be very resistant to ripping and can be reused many times.
The absorbent material you'll put beneath it will vary depending on the weather where you live. Large sponges for large palettes can be hard to get so I use different fabrics depending on the climate. In some places you might need something very absorbent (fabrics like those used for those soft blankets are good, as are old sweaters). But if you live in a colder wetter climate you will probably find your paints get too liquid. In those cases, try to keep the fabric just barely damp, don't close the lid, cover the paints from dust but don't seal them in the container, and try thinner materials such as paper towels, or less absorbent materials. I found this after I recorded the video, but faux leather works well because it's not very absorbent and the parchment paper still likes to stick to the smooth black back when it's only damp (something that turned out to be a problem with the old sweater fabric I used in the video, it would not stick and the parchment paper would curl up and dry).
I also showed a temporary fabric only palettes I made, but that really is a last resort, and I'm not sure how common the fabric I used is.
Finally, I also occasionally use a silicone palette (only briefly pictured in the video in the end comparison) I talk about it here. It was cut from a silicone baking mold. I can't believe nobody sells a palette like this. The paint is very easy to gather into small piles which helps to keep them wet, and if it does happen to dry, it does not start to come off and mix in with your fresh paint like it would in a glass palette. It is hard to find them in neutral colors and harder to clean though , especially the opaque side that I prefer. I usually spray it with alcohol, wipe off as much paint as I can, then go at it with an old toothbrush, alcohol and soap. I plan to find a container to leave it and some of my rags to soak in acetone (which is stronger and will last more uses) in the future.