Binding repair

[Richard500]

The attached photo is an Oscar Schmidt 12 string from probably the early 20th century. In a dozen places the white bits of the binding, which seem to be a thermoplastic (celluloid?) have dropped out.
I can’t think of a simple way to make replacement pieces, but since I’ve seen the same binding on other mandos, someone must have a technique. I’m a little afraid of trying to sand close to that purfling or the edge of the bowl. The profile of the pieces is close to a quarter round.
Use some kind of a hardening filler?
While I’m at it, is there some material that’s used to fill celluloid inlay pieces that have detached other than skill?

[sunburst]

I would buy some matching binding material (ivoroid? white plastic?), cut and fit pieces and glue them in place. Leave them a little large and then scrap them down to size after the glue has fully cured.
The original material might have been some type of plastic, ivory, or who knows(?), but I wouldn't worry about a direct material replacement. Just go for a good color match and touch up the color finish as necessary (almost surely spirit varnish).

[rcc56]

Ditto.

If you know a builder or repairman in your area, they may be willing to supply you with enough material to do the job. If not, you can order binding material from a dozen places, such as Stew-mac or LMI.

If you do order, you will find that the modern plastics will be the more practical choice. That is because celluloid is now classified as a hazardous material, and there is a stiff shipping surcharge on all shipments of celluloid. The other plastics are not subject to this surcharge.

Most people won't be able to tell the difference between modern plastic and white celluloid once you add some colored finish to it.