Can some explain the numbers on art pencils?

Question

I'm referring to the carbon and charcoal ones. I see HB, 2B and I also see things like no. 555, 2BP #597, When do you use charcoal over pencil and visa versa and could you please tell me how these numbers go??

Answer 1

I'm not sure exactly how the numbering system works but I'm pretty sure it has to do with the softness/hardness of the lead.  

Answer 2

well i don't know what the letters mean but the numbers are the density of of the lead in the pencil

Answer 3

I don't know exactly can't remember from being in art which ones are which but they are different shades. Like i think the HB is the lightest shade. You use charcoal over pencil when doing sketch's that require different shading

Answer 4

there is a scale which varies from manufacturers, but generally goes from 9H (H=hardness) to 9B (B=blackness), which refers to the properties of the graphite itself.  A hard pencil gives you a hard line which smudges little and will sharpen to a strong point, whilst moving from grade B through 9B offer you varying grades of blackness or softness, meaning the  depth of tone you will achieve, and the "smudginess" of the mark. There is also an"F" grade (Finepoint) that sits in the middle  of these.

Personally i prefer not to mix charcoal and graphite in the same image as the graphite contains waxes progressively in the "B" range, and charcoal often doesn't sit well with this. If you were to use both together i would suggest using charcoal first, then the pencil over the top for this reason.

Wiki gives a good chart of the pencil grades, and i will put the link below :-)