Flocculating and deflocculating

[Cyndy Littleton]

I am a fairly new potter with a question regarding glazes that separate so badly, it is a constant battle to keep them in suspension. I recently mixed the blue green/ red copper glaze listed on the Ceramic Daily site. It does not stay in suspension long, has to be constantly mixed prior to dipping, and goes on unevenly. I read an article about flocculating glazes and different techniques to help with suspension. But my question is "How do you know how much to add to the glaze?" The article recommended using epsom salts, but did not indicate how much or how do you know when it is too much. Any suggestions?

[Theresa Marie Shanks]

[Cyndy Littleton]

Thank you for the video!

[Chantay Poulsen]

Cyndy,

search John Britt on you tube.  He has another video about adjusting your glazes.  It made a huge difference for me.  I am now able to get my glazes to go on smooth and even with little dripping.  Good luck.

-chantay

[Norm Stuart]

I've found Calcium Chloride more effective and easier to use than Epsom Salts (Magnesium Sulfate).  Calcium Chloride absorbs moisture from the air, and gives off heat as it dissolves in water.  The calcium or magnesium (hard water ions) increase the repulsion between clay particles so they suspend the other glaze ingredients. Adding sodium or potassium shorts-out this suspension.

http://www.amazon.com/s/ref=a9_asi_1?rh=i%3Aaps%2Ck%3Acalcium+chlor...

We bought a 9 pound sealed container for the studio which will last for many years.  For a gallon of glaze we just add a sprinkle of 20 to 30 pellets.

If your glaze does not have at least 10% kaolin, clay or clay-like material such as gertley borate, adding calcium or magnesium ions will have no effect.  Since many glaze ingredients, especially nepheline syenite leech sodium or potassium salts, you need to periodically add more calcium or magnesium ions to offset these salts.

Glazes which simply don't have clay you have two choices.  First add a couple of percentage of veegum or even more betonite.  Even this small amount of calcium charged silica can poison some all frit glazes, like cadmium sulfate reds.  So in  those cases you have to rely on an organic gum like xanthan gum to help suspend the glaze and harden it as it dries.

[Cyndy Littleton]

Thank you! I have used a few recipes from John Britt and have loved them. I did not know he had a video. I will definitely spend some time with it.

[Cyndy Littleton]

Thank you Norm! I have copied this so that I have it as a reference in my glaze lab!

[Lawrence Weathers]

Before Jon Britts video I understood what flocculate and deflocculate  but I wasn't really sure why I cared or what to do with it. Now, I find that it solves a number of glaze problems. However, I can assure you that I only do it in private :)

[Cyndy Littleton]

Oh, I agree!

[Chantay Poulsen]

Well, I posted from my phone, but now it is gone. Working from tablet. CYNDY, if I am having trouble adjusting a glaze I pour out a measured amount, like a pint. I then carefully measure additions, keeping notes. Once I have the glaze right I can then calculate adjustments for larger batch. Hope this helps.

[Norm Stuart]

Remember that you can easily fix over-flocculation with a deflocculant, or the reverse.  So I think it's better approached by feel and texture, sort of the same way I cook except I can't taste test the glazes the way I can with food. 

With a background in chemistry I was very keen on the quantization of things ceramic, but there are a lot of different and opposing factors at work in making a glaze what you want it to be.  Making it a science would be very complex equation.

In Southern California, the mineral content of our tap water varies during on where our water is being sourced. Colorado River water has more calcium and magnesium so glazes are more flocculated.  But when we receive water sent from Northern California there's less far less calcium and magnesium so we need to add calcium chloride.

And some glaze ingredients, especially nepheline syenite, will slowly leech deflocculating sodium and potassium ions into the glaze so adjustments continue to be needed over time.

[Cyndy Littleton]

Gotcha. I have a similar situation here in Western Virginia. We have a lot of calcium carbonate due to limestone leaching. I try to filter the water prior to making glazes.Thank you for all your help.

Norm Stuart said:

Remember that you can easily fix over-flocculation with a deflocculant, or the reverse.  So I think it's better approached by feel and texture, sort of the same way I cook except I can't taste test the glazes the way I can with food. 

With a background in chemistry I was very keen on the quantization of things ceramic, but there are a lot of different and opposing factors at work in making a glaze what you want it to be.  Making it a science would be very complex equation.

In Southern California, the mineral content of our tap water varies during on where our water is being sourced. Colorado River water has more calcium and magnesium so glazes are more flocculated.  But when we receive water sent from Northern California there's less far less calcium and magnesium so we need to add calcium chloride.

And some glaze ingredients, especially nepheline syenite, will slowly leech deflocculating sodium and potassium ions into the glaze so adjustments continue to be needed over time.

[Cyndy Littleton]

Thank you Chantay! I have learned (mostly the hard way) to keep a glaze diary.

Chantay Poulsen said:

Well, I posted from my phone, but now it is gone. Working from tablet. CYNDY, if I am having trouble adjusting a glaze I pour out a measured amount, like a pint. I then carefully measure additions, keeping notes. Once I have the glaze right I can then calculate adjustments for larger batch. Hope this helps.