Grind Marks in Cabochon

Fixing a Mistake with Super Spray

In one of my attempts to fix devitrification on some of my fused glass cabochons I made a mistake. As a result of that I found myself trying yet again to rescue these cabochons.

So what was the mistake? It was to cover ground cabochons with Fuse Master Super Spray anti-devitrification solution. The result was the encasing of what appeared to be grind marks below what is otherwise a wonderful polished surface. I expected the glass to all fuse together and obliterate the grind marks, but I suspect the marks were simply too deep and minute air bubbles were trapped below the surface.

So now I find myself trying again to remove not devitrification, but those encased grind marks.

Devitrification on Cabochon
Devitrification on Cabochon

Here in these photos you can see an example of devitrification and the encased grind marks below a polished surface. The Super Spray worked beautifully, giving the pieces a nice polish, but the grind marks remained.

My initial thought was to simply fire polish them again and see if they would polish out, but I wasn’t sure. I had my doubts it would work. If the marks were micro bubbles of air trapped in  the grind marks them I suspected that, short of a long full fuse, they would not rise to the surface and escape. Not having a lot of experience with this I decided to prepare just a few cabochons and do a test fire.

Grind Marks on Cabochon
Grind Marks on Cabochon

Taking a few cabs I decided to grind back the edges of a few, but still leave some of the encased marks. My reason for trying a few cabs rather than just one was to ensure the result was consistent.

Because the marks extended down under the bottom curve of some cabs I decided to grind the edges slightly different on a couple. One I would grind the edge back until the edge was perpendicular to the bottom to a point where the bottom of the curve was totally removed. On another I ground it back less severely and left a slight curve.

Ground Cabochons
Ground Cabochons

In the photos after grinding you can see the red cab still has top surface marks although is ground around the edge. The others show how they were ground around the edge, though the one on the right was not ground along the top edge.

Ground Cabochons
Ground Cabochons

These were fire polished on a prepared shelf, not shelf paper, and not covered with Super Spray. The firing schedule is below.

After Firing

Fire Polished Cabochons
Fire Polished Cabochons

The fire polish actually worked very well.

The ground edges polished well, rounding nicely and resulting in a polished surface. However, those edges not ground and the marks on the top surfaces of the red one remained unchanged.

Fire Polished Cabochons
Fire Polished Cabochons

This verified what I thought would happen. The encased marks would not polish out. Once entrapped I suspect they are there for good. It will be necessary to grind back all surfaces where there are entrapped grind marks.

Lessons

  • Never coat a ground surface with Super Spray.
  • Ground surfaces will fire polish out without further finishing to a fine surface and without any devitrification solution such as Super Spray.
  • Super Spray works great, in the right circumstances.

Firing Schedule

Fire Polish – Bullseye COE 90 Cabochons

Please be aware that all kilns fire differently and this schedule may not produce the same results in your kiln.

Segment Rate (C/hr) Target (C) Hold (mns)
1. Strain Release 222 537 10
2. Process FULL 732 10
Crash Cool Open Door 550 0
3. Anneal Full 516 30
4. Cool 83 371 5

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s