In pottery glazes, cadmium and selenium are used to create red in oxidation environments, which are the opposite of 'striking'. Striking is similar to reduction firing, where the firing environment is starved of oxygen to achieve the red color. Cadmium and selenium are used in low-fire glazes and are more reliable colors than copper reds. The shades of color look very different however.

I make copper red glazes by using glazes that include copper carbonate and tin oxide and fired in a reducing atmosphere. Copper reds often are a muddy shade.

In general, reduction firings starve the kiln (or glass furnace) of oxygen. The heated fuels combine with oxygen in the glaze or glass batch, changing the glaze color as oxygen leaves and the minerals are converted to different molecules.

I can't really comment on the use of gold to create red glass.