• Make some glass slugs for testing polishing processes

I bought another muffin pan and pre-fired it. This destroyed it. I think the oxide layers that formed were thicker than the metal in the pan. It had the consistency of a Sao biscuit.

I ordered a set of four stainless steel drinking cups from ebay. I pre-fired them. There was lots of black gunk on the outside afterwards, but I scrubbed it off with a wire brush, and then scoured with sand. They were still black, but without loose contaminants. They kept their strength.

I applied a single layer of batwash and dried them on a hotplate. I measured out 130g of crushed glass into each of the four cups and ran them through the same profile as last time:

Initial results were promising.

However during the rough grinding pass one of the slugs fell in half.

A gentle tap with a hammer split another in half too.

I believe there are two problems:

• There are veins of impurities running through the glass,
  • These will create a weak point for a crack to start.
• My tempering profile could be improved,
  • The current profile I'm using was created for tempering float glass. Container glass is slightly different, and so may require a different profile.

• Read this: http://www.glassblower.info/books/TheGlassTemperingHandbook.pdf,
• Read this: https://www.instructables.com/id/Casting-Glass/,
• Read this: http://www.glasskulls.com/asending-sequence/,
• Adjust my temperature profile accordingly,
• Wash my glass in HCl to clean off impurities,
• Make better slugs.