The dust that falls into your easel tray can be used to make new pastels!
Homemade pastels are a pretty easy project, and best of all they might end up being some of your favorite colors because they're made from all the different pastels you like to paint with.
The first thing you'll need to do is start saving your pastel dust. There are two strategies for this: empty your easel tray regularly, separating dust by color family into different jars (e.g. blue dust goes into one jar, red into another) or collect all the dust in a single jar, no matter the color. If you collect dust in one jar the new pastels you make will probably be in the gray family. That's what I did.
Once you have the dust all you need to make new pastels is distilled water, an eye dropper, gloves, a palette knife, and a dust mask. You'll also need a surface to make the pastel on, like a table covered with glassine, aluminum foil, or parchment paper. A piece of glass from a picture frame, or a plastic paint palette would also do nicely. Basically anything flat that you can either throw away or clean after making the pastel.
Safety Note: The process of making a new stick can put fine dust into the air, so I recommend doing this project outside, while wearing a dust mask. I also like to wear gloves.
Step 1- Pour dust onto your flat surface. It takes a pile about 2.5 inches in diameter to make an average-sized stick. If you have a large amount of dust you can make several sticks at the same time. Dust that comes from your easel's tray is likely a very fine texture already, but if there are any large chunks, grind those up or remove them.
Step 2- Add a few (seriously, just a few) drops of distilled water to the dust. Use a palette knife to mix the water and dust for 1-2 minutes until it becomes a clay-like texture.
At first the mixture is going to look too dry and you're going to want to add more water, but don't do that yet! Keep mixing, it takes time for the pastel pigment to absorb the water. If after a minute or two the dust is still too dry, go ahead and add another single drop of water. Mix and see if that's enough, if not add another drop of water, then mix. Keep repeating this process until the texture is correct.
In this picture I have enough water, I just need to mix a bit more.
Adding more water too soon greatly increases the chances of ending up with a soupy mess instead of the clay-like texture that you're aiming for.
If at any point things get soupy (like in the picture below) don't worry, just let the mixture dry out a little. Check it after 10-20 minutes, by mixing it it around to see if it's clay-like yet. If not, wait a little longer, it will get there.
Step 3- Once you have your pastel clay, form it into whatever shape you'd like. Round and rectangle are the most common, but you could make anything you want. At this stage the pastel you make is going to look very lumpy and bumpy, that's O.K. we'll refine it in the next step. Once you have the desired shape leave it to dry for 10-30 minutes, depending on the weather (if it's dry and warm outside you'll need less time than if it's humid and cool).
When I first tried making pastels, I thought steps 1-3 was all there was to it, so I'd stop here and let the pastel dry into a lumpy bumpy mess. I never liked those homemade pastels because they were uneven and I couldn't get good mark making from them, so I decided saving dust wasn't really worth the trouble. It wasn't until I figured out steps 4 and 5 that I was able to make good quality sticks that painted as well as my store-bought pastels.
Step 4- Once the surface of the stick looks less shiny and feels less tacky (typically 10-30 minutes, depending on weather) it's time to refine the shape. If you've made a round stick just roll it some more and the surface will get smoother. If you've made another shape like a rectangle, use a palette knife to smooth the sides. Then it's time to let your pastel to dry for 1-2 days. I usually move mine inside to a flat surface that's out of the way, so it won't be disturbed or broken while it dries.
Step 5- The last and final step is to sand the pastel stick so each side is smooth and even. This can be done with actual sand paper or a scrap of sanded pastel paper (which is what I usually use). Sanding is optional, but it makes a nicer more professional pastel. If you skip this step you won't get completely even mark making from your new stick until the sides are worn down from use.