Well, as promised in the topic about Ester Roi, I am reporting back my results of using a food warming tray to activate colors. (Boy...I am no Ester Roi!

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The top two demonstrations were done with
Prismacolor colored pencils. These are soft, wax-based pencils--very creamy. The image on the left has been burnished by placing the paper on a food warming tray on the highest setting and using a paper stump to burnish it. The pencils did melt somewhat, but I could never seem to get the color well into the tooth of the paper. The image on the top right was done by burnishing the colored pencils with a paper stump dipped into baby oil. Much better result.
The bottom two images were made using
Caron d'Ache Neocolor II, a Swiss product that is a water-soluble wax pastel. They look and act like crayons. I had the same issue with the heat--it never melted the medium enough to get it into the paper. The image on the lower right is with the same crayons that were activated using a damp brush and clear water. I could move the color around a little bit--unlike any of the other options--and it felt like watercolor.
Lessons learned:
1. My food warming tray got quite hot, but maybe Roi's tray gets even hotter (?!) Also, I know I wasn't as careful as she was about going painstaking step-by-step when she demonstrated how to do the pebbles. I was just eager to get some comparisons done.
2. When working with this sort of medium, it might be better to use a smoother surface (I used Arches 140 lb cold press paper), like a hot-pressed paper.
3. If you press too hard when transferring your drawing to the paper, you will end up with indentations on the paper that can be a little hard to fill with color.
4. I prefer my watercolors to these. I like to be able to see what my results will be, rather than laying down color and then using something to burnish--heat or baby oil or a solvent or water--to see what the final result will be. I don't like feeling that I was giving up that sort of control.
5. The watercolor crayons are actually rather fun, and I think they could be used successfully to handle some backgrounds. I'm going to try them for this.