This is great, I too have dermatographia - people always comment on how painful it looks when all I've done is just scratch myself - it doesn't hurt at all! Its just itchy.

... as for the suggestion for using it in exams...LOL... i am a medical student interested in dermatology so it may come in doubly handy!

The art is an interesting idea - i especially like the last picture - it really shows off the textural contrast of the welt without the surrounding redness.