Often what the eye suggests is black isn’t really black. Much glass–not Carder’s–is a dark amethyst that because of its thickness appears black, except when held up to the sunlight. Technically it is what is called Black Amethyst. Lon Knickerbocker amplifies on Carder & Sinclair’s versions of mirror black.
I seldom put much stock in Erickson (ed. referring to Eric Ericson’s book on Carder’s colored Steuben Glass)- however in this case Randy Blye is correct. I have had many so called experts suggest that Steuben’s mirror black is the only true black glass made- which is false. Max Erlacher recently shaved two pieces of mirror black of mine- because I was trying to prove a point and yes they are, purplish red. Some may find it interesting that Sinclaire’s black can also be this color- or green or blue tinted.