My current favorite is a Sanford Design Drawing 3800 8B, drawing pencils
and sketching pencils seem to put down an even darker line than drafting
pencils for the "same" hardness, (just like paper grades all 8B pencils
are not alike) and some soft pencils have hard bits in the graphite that
feel terrible when writing on a smooth surface like the back of RC
papers--to me its like the sensation of chalk screeching on a blackboard.

Sharpie's OK for RC, I don't consider the work I do on RC to be
"permanent" anyway so I mark up both the front and back and if I need a
cleanup, PEC-12 takes Sharpie right off the front of RC prints.

darkroommike

Nicholas O. Lindan wrote:
A #8B Faber-Castell 9000 pencil does a good job of
making notes on the back of RC B&W prints. I like to
jot down exposure data when I make a print so I can
make some sense of the printing session on the next
day when examining the dried prints.

I had been using a Sharpie marker but never liked it.
Used on FB paper the marker can bleed through, so I have
to keep a pencil handy in any case.

The pencil makes nice light marks that stay on and don't
smear. And it just 'feels better' than a marker.

Additionally the pencil won't mark the front of RC paper
so I get confirmation that I am not about to print on the wrong
side of the paper.

Available at art supply stores and via Amazon. Around
$0.80 each.