PENCILS AND CRAYONS
As I've said, the way I prefer to approach lithography there are no "rules" which govern how to draw a plate or stone. However, when teaching I stress that there are approaches which are more or less predictable than other processes.
Drawings made with crayon and/or pencil are relatively easy to process and print because the number on the crayon or pencil gives you a very good idea of how much grease is in the drawing so you can figure how much etch to apply - the pigment in these types of drawings is a direct indicator of the greasiness of the drawing as long as the crayon/pencil has not been smeared around or combined with other media.
I have heard good arguments for both drawing with soft crayons first and for drawing with the harder crayons first. In theory I prefer drawing with softer crayons first as I like pushing the grease of these crayons around with the point of a harder crayon or pencil later. Some printers insist that if you draw soft crayons over hard you'll have difficulties etching the work, because there will be a lot of greasy drawing on top and a lot of less greasy crayon underneath which could lift off during etching. If the image I am working on changes and requires a broad area of soft crayon over a patch I had rendered with a hard crayon then I will readily do so without worrying about technicalities. I have heard this matter defended and debated from both sides and cannot suggest which is best: I know for myself that I have had no problems working either way. If I was working on a photo-real rendering where I was tremendously concerned with tones printing identically to my drawing, I would probably just use one or two closely related numbers of pencil.
Currently there are two kinds of pencils on the market; the more traditional choice is made by Korn's; the pencils resemble grease pencils but are far more carefully made; they come in numbered increments between 1 and 5, 1 being the softest and 5 being the hardest. The same company also makes crayons (about the size of a conte crayon) and tablets (about the width of five crayons) ranging from 00 (extremely soft) also to 5. Korn's products are water-soluble and the pencils need to be sharpened with a razor blade or with a small hand held pencil sharpener (which won't be useful for sharpening much else since the grease will clog it up somewhat).
The other kind of crayon, recently put on the market, is made by Stone's; theirs in not water-soluble (and so can have washes floated over it without disturbing any rendering) and comes in crayons, tablets, and thin sticks which require a`plastic holder to use. Each has its advantages; being used to Korn's I know how to work around their water-solubility and sometimes use washes to dissolve and remove unwanted crayon marks, but I like the idea of a mark that will hold up under a wash.
Another pencil which works on both plates and stones, although not specifically made for this purpose, is a Prismacolor black colored pencil. It is convenient to draw with and to sharpen and can produce delicate effects (not that the other pencils can't, but for beginners grease pencils and crayons are hard to become accustomed to, and the prismacolor seems very familiar and easier to handle). Prismacolor can be used with any other litho drawing medium and like Stone's crayons is not soluble in water. There is very little grease in a prismacolor and it requires no acid during the first etch -- it is very easy to burn out or lose light passages so I would suggest over-drawing (adding more tone than necessary) to insure the results you want. During drawing do not rest your hand on your plate or stone - the grease in your skin (anyone's skin) will affect your drawing. Use either a bridge to rest your hand over the drawing surface, or a clean piece of paper.
From the Stone and Plate Lithography Lab Manual by Lise Drost, Greenwall Press, 1992