How Rubina Verde Hobnail Was Created The glass used in the production of Rubina Verde was "Heat Sensative" Vaseline Glass, and "Heat Sensative" clear "Flint Glass". That means that real Gold was used in the batch when the Vaseline Glass was made in in the furnace and Phosphate was added to the Clear Glass in the furnace. The process required two trips to the Glory Hole to produce this type of Art Glass. The worker starts with a gather of Vaseline Glass which he allowed to cool slightly. Then he returned the gather into the furnace to "Strike" (reheat) the glass to change a portion of the gather to a Ruby color. Next the worker brings the gather to a shape mould and blows the gather into the mould that forms the basic shape of the pitcher. He removes the formed shape from the mould and goes back to the furnace to a different pot of heat sensative clear glass that has phosphate in it. He quickly places the ball into this glass to get a new layer of clear crystal on the surface. The worker then brings the pitcher shape to the finishing mould and blows the ball into it's finished shape which now has the Hobnails on the surface. The worker then returns to the furnace again a second time to "Strike" (reheat) the clear glass surface of the pitcher to change the hobnails white. Striking is a chemical reaction that only occures once. The ruby color was already struck once so it will not change any further. On the second striking, the worker is is only changing the color of the clear glass to white. So it's the hobnails which are closest to the heat as he spins the ball and it's the hobnails that turn white. The piece is then handed off to the finisher who will shape the top and apply the handle. By understanding how colors were made, you'll begin to understand how some of the very elaborate patterns were created in Opalescent glass.