Re tested the scales and they are faux ivory. I didn't get the needle hot enough first time around and in my defence they were collar less.
I have many ivory scales that are thin but I also have one which is thick , probably because it was carved therefore needed to be thicker . doh

The YSC stand for Yorkshire Steel Company and I guess 423 is some thing to do with them also.

Whether or not its is SS remains to be seen. Until I hone it which could be a long way off. I have a queuing system
Cheers