I use the tracing paper, it is thin and does not damage the "skin" on the intonaco. Charcoal dust works fine to the point that i would wish to have less charcoal coming through, even with the fine pouncing wheel (large pouncer is to big for the fine detail). I do a small rendering, then transfer it to actual scale of a fresco onto the paper for the preliminary composition "to scale study". Then I make tracings and transfer on the new paper for the final cartoon. After the final is done, I make the new tracings for the fresco and reuse the old tracings for the sinopia.
I bit too many steps, the one may say, but lately I do the same even for the regular murals (except the "to scale study") - I call it the fresco method. Gives great results - after client sees the cartoons I have no "double checking and making sure" - I left along to paint in peace.

I have to show how to tell that the plaster is ready for the transfer - "picture" worth a thousand words, as people say - you can not measure it must be felt by fingers.
Alert! commercial interruption - our workshop link http://www.truefresco.com/workshop.
Also Ian (the plasterer) tells me when to start. Other ways you have to do some experiments, remember different paper gives different clues, make sure that paper does not "pull" the water from the plaster, this "pulling" will kill the "skin".

Gary, I really like those two girls!

Yoram, looks like you've built an outstanding reputation for yourself - from the sketch onto the wall, impressive. Any tips?

Ilia
http://www.truefresco.com/anossov