First you will need a rectangular silicone mold. I was looking for a way to make our own Block Crayons for quite a while, I was searching for the perfect mold shape that would allow us to make a bunch of crayons in one shot. I really struggled to find something that fit the bill. I've see a few people use plastic molds from eraser packaging but this seemed super labor intensive - making one at a time. I stumbled across this mold accidentally, somehow all the searches I did came up empty and finally while mistyping a search term this popped up! Order one for yourself here!
Start off with new or old crayons, make sure to sort them out by the different brands you might have in your stash. Any non-crayola crayons do not do well in this project - cheaper crayons tend to have way more wax and the wax separates out from the color. So if you need new crayons definitely grab Crayola Crayons.
Start the project by prepping them to peel by placing some warm (NOT hot, they will melt and you will have a mess) water and a pump or two of dish soap into a baking pan. Lay out your crayons and let them soak for a few minutes. After a little bit you'll notice the paper will start to peel off of the crayon and you will be able to easily slide them out or unravel the paper. If you notice that your crayons aren't peeling try added some more warm water to your tray. If you would like to do a natural version of these using beeswax and natural pigments +The Hippy Homemaker has an awesome recipe on her blog.
Preheat your oven to 200 degrees.
Once your crayons are peeled and dry you can begin placing them in the molds. Fill them high! If there are a bit higher than the top of the mold that is OK the crayons will settle when they melt. If you don't fill them enough you will end up with tiny, thin crayons that will probably break when you try to remove them.