I have a question in regarding to James' Victory Halogen Infrared Ruby Slim Vertical.

Which Copper Oxide was this doped into the envelope?  There are several listed at https://en.wikipedia.org/wiki/Copper_oxide

I am not sure which oxide was added to the quartz melt, however after drawing the quartz tube it exists in the form of Cuprous Oxide which has a slight reddish colour.  It is probably not Cupric oxide because that is black.  After reducing in the hydrogen furnace, the oxide is converted to nanoparticles of metallic copper whose particle size and distribution is such that they create the deep ruby colour.  Same as in natural red coloured glass.

Thanks, James