I have heard instructors tell their students to put a stripe of
Sharpie pen ink on a piece of silver to be annealed, and when the ink
disappears during heating, that is a sign the silver is annealed.
I don’t subscribe to that technique, personally. I have had students
who did that, but their sterling silver never got hot enough to be
truly annealed. So, rather than look at ink on the metal, I advise
watching carefully for the silver to get a dull rosy glow, to be
really annealed. In my studio, I use a small metal box, lined with
Solderite boards, for doing our annealing. (I use an Army surplus.50
cal. Ammo box with the lid removed, turned on its side. It’s size is
just perfect, and made of heavy steel.) In that way, using a torch,
the metal being annealed is in an enclosure in a “shadowed” area, so
seeing the metal’s true color is much easier than annealing in
normal room light.
I use a Sharpie pen all the time in my studio, for marking on metal.
For instance, when marking a line on a sheet of metal, I will color a
field of black with the Sharpie, which dries nearly instantly, and
then I can scribe a fine line into the black Sharpie ink field. This
line is perfectly accurate, and won’t rub off while working. The ink
removes easily with alcohol and a rag.
I have Sharpies all over the studio, for easy access.