I spent a lot of time researching a satisfactory replacement for the trusty Dixon Tru/Color Vis-aid pencils that we used for many years. The pencils were labled Tru/Color Film Marker Black 2225 while the box says Vis-Aid Film Marker Pencils 12225. I have some Dixons for sale in one of my other auctions.
I like these pencils better than the Dixons. They make a fine dark line. They are slightly softer and need a lighter touch but they won't damage the film like the Dixons did if you got too sharp of a point. I wrote about these pencils as well as other contenders in an article called "For Doctors: Dixon X-ray Pencils Discontinued."
For a while, NUCCA was recommending a pencil by Steadtler. Don't waste your money on those. They are more like a woodcased china marker. Too soft for accurate marking.
I've given these to some Dentist friends who loves them.
These write on x-ray, glass, plastic, wood and metal. Wood carvers will also use these.