Cel numbers fading

I have 2 layers of cels which the numbers(and letters) are actually fading. How long does it take for the cel numbers to actually fade? I want restore the numbers since no sketches came with them. Is there a special pen I could use to do this or do I just use a sharpie?

Regular permanent pens are pretty volatile. They do make marker pens specifically for marking on photos. Those should be ok and you can probably get one in any good crafts store (check the scrapbooking department. That section is a motherload of useful stuff!). Alternatively, perhaps the fine markers used for marking CDs would be good. They're supposed to be permanent too.

Wow, I've never heard of cel numbers fading... that's odd.

I would be wary of marking over them again, since it could make things worse and also possibly affect the value of the cel.

Agreed, I too would be wary of editing the cel number original markings. IMO do not do it, I have never done it any of my cels regardless if the numbers are fading or almost faded. Good luck with whatever you decide.