Silicon carbide bubbles

[Barbie]

Hey guys, I have been making lots of glazes all at cone 6 but every time I do anything with silicon carbide to get a pseudo copper red effect it gets all bubbly. It looks kinda frothy. I've experimented with a couple of bases but without fail it froths in the kiln. Looking for some debugging on this. More hold time at specific temp? More flux? It's a super fine mesh, I got the finest I could get my hands on. Any suggestions?

[Hulk]

Hi Barbie,

Have you seen Tony Hansen's entry on SiC?

"SiC powder has some curious uses in ceramic glazes. It is employed to make crater and foam glazes. The silicon part takes up available oxygen to make SiO2 and the carbon combines with oxygen to make the CO2 that creates the blisters and bubbles. Using this mechanism it is possible to create reduction effects in oxidation firings, but with obvious challenges (blistering and bubbling). The carbon that silicon carbide particles release acts to reduce metallic oxides like iron and copper. Additions of tin oxide will aid color development, especially for copper reds. The Potters Dictionary has a good description of this.

There is some question about how to include SiC in glaze chemistry calculations. Perhaps that best answer is not to do it. Treat it as a recipe level additive (having predictable effects as such) while looking at the rest of the ingredients as suppliers of oxides to the glaze that the SiC is affecting."

from https://digitalfire.com/4sight/material/silicon_carbide_1250.html

 

There are a few threads here as well, please see

https://community.ceramicartsdaily.org/topic/4341-silicon-carbide-in-glazes/

   which includes links to articles that may be helpful, as well as on topic comments.

[Min]

 

1 hour ago, Barbie said:

It's a super fine mesh, I got the finest I could get my hands on.

What size is that? Needs to be extremely fine, in the 800 mesh range. The Tom Coleman article that's mentioned in the link Hulk posted above is really very good, well worth the read. 

[Barbie]

Thank you for your prompt responses. I now have more research and testing to do. I really appreciate the help.

[liambesaw]

I have FFF grade (it's 19 microns, smaller than any mesh).  I still had some bubbling on a few copper reds I tried, but I also have some gassy clay bodies.

[Min]

Good point Liam about the particle size of the silicon carbide. Tom Turner spoke of mesh size up to 1200 and used Washington Mills as his supplier. Washington Mills  have a conversion chart of microns, Tyler sieve size, micro-grit  etc. They are now listing the sieve size up to 325.

[neilestrick]

Lapidary suppliers carry the super fine SC.

It's really easy to get too much into the glaze. I've played with it a little bit, and always got bubbling as well. I've always wondered if it would be worth trying to do it the way I fired gas kilns. When I put the kiln into reduction at cone 08, I always stalled it for 45 minutes, then put it into a more neutral atmosphere and let it climb. I wonder if doing a hold at 1850F would give the SC a chance to burn out some and reduce the glaze before it got hotter and the glaze melted around it and caused bubbling.

[Magnolia Mud Research]

The amount of SC needed is proportional to the copper (molar basis) , the SC is the reducing agent for the copper oxides  .  If the SC is significantly higher than the  amount to reduce the copper the the melting glaze will convert the SC to silica and gas.   Careful testing well help.  The glaze also needs to not be very stiff or the gas will make a mess.