When analysing the contacts to find the frames one wants to work with, I have seen that some use some sort of white or red marker both to circle the interesting frame, and also to indicate cropping.
I just can't figure out which type of pen/marker is used that both sticks to the smooth contact surface, is opaque and does not rub off. A permanent ink-marker obviously wouldn't work since it is transparent, and wouldn't show on black background.
You need the same type of pen that is used to write on overhead projection slides. The have a spirit based ink rather than waterbased. Colour is your choice, I find blue and black shows up well under safe lighting as well as normal room lighting.
They are called "grease pencils" in the US, or sometimes "China markers". Sanford makes them in many colors, and I think Stabilo has a similar product in the EU. A quick Google will get you started.
They are called "grease pencils" in the US, or sometimes "China markers". Sanford makes them in many colors, and I think Stabilo has a similar product in the EU. A quick Google will get you started.
I use a chinagraph pencil, black. It is also very handy to mark the groundglass screen on my F3 for alignment.
Below, is a quote from a website selling chinagraph pencils.
"The original pencil for marking on glass, acetate, film, china and all impervious surfaces. Impervious to water it may be easily removed with a dry cloth."
Very handy, low tech, doesn't dry out, quite cheap as well.
My guess is the description in the OP was of china markers and that an erroneous assumption was made that what was observed, would not rub off. China marker can be rubbed off but it takes deliberate effort. It doesn't come off casually.
Any of us who can remember using brushes in a signshop probably have dozens of stabilo's floating around, I just looked and in 30 seconds, found 6 blue and one white.