Tried a clear base color over a dark one and got a weird foggy effect

I was working on a simple vase last week, using a dark cobalt blue as the base. I wanted to add a clear layer over it to make it shine more, so I picked up some standard clear frit from the shop. After I put it on and worked it in, the whole piece went from a deep blue to this milky, foggy gray. It looked awful, like I had mixed in some kind of white powder. I let it cool down and checked my notes. Turns out, the clear frit I grabbed has a slightly different COE than the cobalt rod I started with. I think the mismatch caused a tiny bit of devitrification right at the join. It was a real bummer, but now I know to double check my batch numbers even for 'clear' stuff. Has anyone else had a clear coat ruin a color like that?

2 comments

2 Comments

samf9517d ago

Man, that's the worst. I've had a clear top coat go cloudy on a dark red piece before, same deal with a slight COE mismatch. It feels like all that work just gets ruined in the last step. You're right to check the batch numbers, I'm religious about it now even for basic clears.

rowangonzalez17d ago

What's the COE difference between your blue rod and the clear frit you used? I've seen that milky haze happen even with a small mismatch, like 90 vs 96.