Glaze Viscosity

[ronfire]

I am finding that I am getting run lines when I dip my pots. I never used to have this much of an issue.

Is this because my glaze it thicker than it used to be? It is hard to tell the viscosity with out the experience so I purchased a NK-2 viscosity cup to get a consistent glaze but I need to find the right viscosity first. Right now I get 8.10 seconds for the cup but that won't mean much until I find the right viscosity and time it again.

 

I am using a clear stoneware glaze on a 04 bisque fire to ^6. 

[Dick White]

What is the specific gravity of your glaze slurry?

[ronfire]

Here is the link to the glaze

 

http://digitalfire.com/4sight/recipes/plainsman_cone_6_m340_glossy_transparent_liner_115.html

 

When I mixed it to the specific gravity I found it was way to thin coating and viscosity so I added more than specified.

I know I can add more water to thin this glaze back down but will it create more or less runs before firing. 

This glaze does not move much when fire to ^6.

[High Bridge Pottery]

'The slurry needs to be slightly gelled to achieve this'

 

Can't seem to spot the SG in that link.

 

 

[Dick White]

Ok, High Bridge beat me to it. Mix your glaze slurry back to the proper specific gravity and then flocculate it.

[ronfire]

So even if I added epson salt to thicken it I can still bring the glaze back to the specific gravity and then flocculate with epsonsalt or vinegar to gel the glaze?

[High Bridge Pottery]

I would assume how much a glaze is flocculated wouldn't change surface gravity so I would say yes. Never noticed the SG change between no vinegar and vinegar.

 

Could be wrong.

 

I have found adding too much vinegar can make the glaze crack off the pot easily.

[Callie Beller Diesel]

Joel is correct. Flocculating a glaze with vinegar or Epsom salts changes the application properties of a glaze, not the ratio of water to dry glaze, which is what specific gravity measures. Tony Hanson advises mixing glazes quite thin, and then adding some sort of flocculant so that the glaze stays somewhat fluid on the pot a bit longer. This gives the application drips a chance to smooth out. It's a technique that's good for glazes that don't move much in the kiln.

 

Edit: adding the flocculant makes it so the pot absorbs more glaze while staying fluid like that. It's why you're supposed to mix it kind of thin. Your pot gets the right thickness of glaze on it while being more user friendly in the bucket.

[MatthewV]

Just like how you need to have earthenware clay and earthenware glazes for an earthenware firing, the glaze viscosity is part of a system of how you apply glazes. What you are personally comfortable with and what gives you good results will not be the only way to do something!

 

I personally mostly use bentonite to help keep a glaze in suspension but it has to be added when mixing the dry ingredients and not after the fact. I keep my buckets on the thicker side (SG= ~1.5 on most last time I checked). I wash my bisque ware under the sink a few hours before glazing or will lightly damp sponge to prime the surface. This is what works well for me.

 

Here are some of the main factor influencing glaze application: clay body porosity, wall thickness, glaze specific gravity and glaze viscosity. The washing of the pieces changes the body porosity, the wall thickness is dependent on how you make your work and the last two are influenced by what is actually in the glaze slurry. When all four are working in harmony, good results will come.

[ronfire]

Thanks for all the knowledge. Guess I will try my next batch of glaze diferently.

Might also try to change a small amount of this glaze down to the SG and then add some vinegar to thicken it up and run a test mug.

[rayaldridge]

I went to a Tom Coleman workshop this weekend (so I can no longer claim to have never been to a workshop) and he said he adds a little antifreeze to his glazes to improve their application.  He also puts a little muriatic acid in his glazes.

 

I would assume the latter is a deflocculant.