'That's made with What?'

Fun Fact from Eye Candy Glass Art:
Do you know how they produce the beautiful glass colors used in stained glass windows and other art pieces? The answer is additives!
Soda-lime glass, as it is called, made with sodium carbonate, silica, lime and some other ingredients, is normally clear. So what adds the colors you ask?
Well, that is a complicated question. Depending on the element added you get different results. For example, Cobalt produces a blue, Nickel produces violet or black, Silver creates an amber to orange color. But the most interesting to me are the pinks, reds, and oranges. Can you guess what element creates those colors? To give you a hint, it is very expensive and thus causes those pieces of glass to be more costly, AND you probably have some on your person! Can you guess ----- it's gold! So if you see stained glass in a vibrant pink or red you can be sure it's made with gold.
(and yes the included photo is a snippet of a window I am currently building with those beautiful pinks). Stay warm!