Horn or plastic frog

[Guido]

Old(ish) bow with tombac mounts. I think it would pre-date good enough plastic but could be wrong. Is this most likely horn?

Are the cheap new Chinese ones of this look now plastic or still horn?

[Guido]

... had a quick look: the ebay specials of the day ($25 and up) all claim to be made of ox horn.

Maybe frogs in horn look were always real and never made of plastic?

[The Violin Beautiful]

If it’s an old bow, there’s a good chance the frog is made of celluloid, which was popular for imitation horn or ivory frogs at the time. You can see similar results in old fountain pen barrels. Here’s a link to a modern pen made in that style:

https://www.stjohnspens.com/shop-pens/omas-arco-bronze-ogiva-fountain-pen-vintage-flex-ef-f-14k-gold-nib

[GeorgeH]

You tell the difference with UV light. See:

https://www.gia.edu/doc/SP06A3.pdf

[David Burgess]

https://www.scientificamerican.com/article/a-cat-turned-milk-into-popular-plastic/

[Guido]

17 hours ago, GeorgeH said:

You tell the difference with UV light. See:

https://www.gia.edu/doc/SP06A3.pdf

Thanks. Now I know it's neither tortoise shell nor plastic; but could still be made from horn, cheese or wood.

The tinsel is probably a radioactive.

[GeorgeH]

2 hours ago, Guido said:

Thanks. Now I know it's neither tortoise shell nor plastic; but could still be made from horn, cheese or wood.

The tinsel is probably a radioactive.

Based on the reference pictures in the article, that looks like cellulose nitrate to me, but I have very little experience with non-ebony frogs.

[Guido]

Actually looks more like casein formaldehyde (6), but I still don't discount horn (1) based on the tiny sample in this study.

Might be good to know if any of these are not suitable for bow frogs (e.g. strength), or what was actually mostly used for frogs and reasonably available to bow manufacturers at various times.