Curious Mk.IV question

I've been spring cleaning my Martini Henry rifles....these guns from the Nepal cache I have discovered that a periodic tear down and rust inspection under the wood is a good idea.

Anyhow....I got to looking at my Mk.IV rifle and couldn't quite decide what the stock plug was made from...the short lever plug from the lever socket removal. Is the plug made of really dark black wood or is it bake-lite/plastic??

Thanks HT