Water Soluble Graphite
Experimented with water soluble graphite pencil, and also crayons, today. Now I imagine for water soluble graphite, the brand does matter more than your brand difference pencil to pencil ( Although, I do feel like I can tell the difference between regular pencils ... an off brand art pencil, and a good one. I have used these ones which are a weird brand 'fine touch ' and they aren't the same. The tombow ones are different from the Derwent ones. ) ... anyway , the Derwent one is good. It seems like thou could probably use this to draw your watercolor drawings and , unless you left a really heavy amount of lead on the paper, it'd probably blend out ( 'lift ' ) easily enough and you'd look like you had at most, the ghost of a pencil line . Normal pencils don't erase from under a layer of wtercolr paint ... despite the insistence of Grant and mike. They were both wrong.
As for the crayons , there's some cool effects and potentials I guess, probably especially if it was a hard oil pastel instead of a crayon . But crayons are what I have and pastels are a pain. I know I've seen preliminaries or thumbnails ... you know, the plan for a painting ... using crayon by frazetta. Its not usually the most ideal effect, but it is an expedient since you can easily apply a watercolor wash over it... so you could sketch, for instance, in crayon, the silhouettes of a crowd of people in the distance and then do a wash over it for a background detail. Also, you can use it to create bright lights like a machine light or something and then wash a color over it. Also, the crayons are really bright. Its cool to create a contrast effect where you use a crayon color that will pop out amongst a watercolor wash. Lastly, the white crayon could be used as a kind of poor mans frisket , so that once you've painted something, you could go over the edges or even the whole thing maybe, with wax so the next details don't mess it up. One of the hassles of a wet in wet technique ( which I like ) is that without a frisket, you're liable to wash away or mess up shit. But when the water hits the wax, it acts like a gate and bunches up against the surface tension.
You can use the water soluble graphite as a kind of cheap shading if you don't mind it being gray , and then blend it. Also, I think its notable that if you were doing a picture all in gray, this stuff would have god level properties in the hands of someone who also knows how to use watercolor . See, you can draw , then erase. But if you apply water, what you've drawn becomes permanent. You can then draw, and add value to that, and erase that or choose to keep it by applying water. So its got potential for control on a level that it seems like no paint really has. Not really something I'd use it for because I'm just not the fussy type ... I like to have done with it .