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====== What I want to accomplish ======

  * Make some glass slugs for testing polishing processes

====== What I've done ======

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:

{{:projects:glass_sphere:work_logs:pasted:20190220-123604.png}}

Initial results were promising.

{{:projects:glass_sphere:work_logs:pasted:20190224-052205.png}}

{{:projects:glass_sphere:work_logs:pasted:20190224-052232.png}}

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

{{:projects:glass_sphere:work_logs:pasted:20190224-052420.png}}

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

{{:projects:glass_sphere:work_logs:pasted:20190224-052502.png}}

{{:projects:glass_sphere:work_logs:pasted:20190224-052532.png}}

{{:projects:glass_sphere:work_logs:pasted:20190224-052547.png}}

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.

=== Video ===

{{youtube>PNHmRhPuz8g?large}}

====== What I want to accomplish next time ======

  * 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.
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