Today's pairing with thermofax screens is Water Soluble Wax Pastels. I use the Caran D'Ache Neocolor II Water soluble ones but other brands should work very similarly. I am sorry I don't have a link for these but you can purchase them from most art supply stores. The larger ones are harder to find and I am not sure they are even made currently as I haven't seen them in years.  They are not inexpensive but they do last a long time. 

 
With these crayons you use textile or matte medium to dissolve the crayon as you pull it through the screen. I can't remember exactly where I first learned this process but it might have been in a magazine article by Susie Monday. Have fun and send me photos of what you create so I can share the love. 
 
I have some new screen designs waiting to be finalized and hope to have them up soon in the Thermofax store.