• Make some glass slugs for testing polishing processes

I welded a steel plate on the bottom of a steel cylinder to make crushing glass easier. I crushed, sieved and rinsed some more bottle glass. Approximate particle range between 0.5mm and 15mm. I soaked the glass in some 30% hydrochloric acid for a few hours. There was some fizzing upon adding the acid, indicating that there was something reactive being destroyed. I poured the acid off into another bottle and rinsed the glass in tap water.

I strained off the water and soaked the glass again in distilled water. I dried it on a hotplate and measured 130g into four batwashed stainless steel cups. I fired them on a new profile. Step setpoint to 1000°C, wait an hour, step to 560°C, wait ten minutes.

The slugs came out with a smoother top than any previous attempt, with a clear concave meniscus.

I also put two slugs from the previous run into the furnace at 560°C for ten minutes to re-temper them. I ground the edges round and have begun to flatten the top and they haven't cracked yet, in contrast to the two slugs that were tempered at 510°C which cracked during grinding.

Roughing down the flat faces on the linisher went better with the correct tempering. Using a jig and a weight I was able to get the slugs to a lappable state much faster.

• Hand grind the slugs smooth