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mrcasey

Deflocculate Or Add Water?

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Deflocculating a glaze may leave you with an unperceived amount of chemicals on the surface as you are glazing. The glaze will seem thinner but actually have a higher chemical density which could give you too much glaze on the surface causing big problems. Usually a glaze thickens as it get used or loses water content by evaporation. I think adding water in better than a deflocculant.

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Here is a simple way to determine the SP (specific gravity) of your glaze.

https://www.amaco.com/clay_how_tos/207

 

I would recommend not using a deflocculant because it is difficult to undo it once added. Adding water is a much more simple remedy.

 

Marcia

douglas and Pugaboo like this

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I haven't come across very many glazes that need deflocculating. MrCasey, is this glaze really high in gerstley borate? If it is then it might possibly need deflocculating, glazes really high in iron oxide (like above 15% or so) can really gel up in the bucket also. Sometimes just letting the glaze sit for a couple days for any soluble salts from other materials to defloc the glaze slurry is enough. A super general ballpark figure for a highish SG would be approx 1.5  I'ld add water if your glaze is above this, dip test tiles with 1, 2 and 3 dips and see if it cracks  or crawls during drying and firing,

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     If I had it to do over again, I'd calcine 1/2 the kaolin and not add bentonite.  I certainly wouldn't use this new 

sodium bentonite that makes gelfromhell.  The reason I added the bentonite is because it says to in Britt's recipe. 

 

 

John Britt's 3M-4 Matte with 5% gray mason stain

 

Custer Feldspar 6 %

Silica 8 %

Wollastonite 20 %

Kaolin 40 %

Frit 3134 12 %

Talc 14 % : 100%

Mouse Gray M. Stain 5%

Bentonite 2 %

 

The first s.g. measure was 1.5 which was crazy thick.  It looked fine on a test tile but gave some of the other studio members some serious crawling

issues.  People asked that I thin it out.   So I did.  It crawled again, so I thinned it some more.  I just kept adding water until I got down to an amazingly low s.g. of 1.25.  At 1.25, the stuff is the thickness of heavy cream and still crawls.  On top of all that, it flows a bit too much and becomes streaky.  

 

My new plan is to actually take some water out and then deflocculate with darvan 7.  If that doesn't work, I'm stumped.  

 

I'm a little annoyed that my little 2" X 3" test tile didn't reveal any problems.  TEST TILES SUCK! 

 

    

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Test tiles the same thickness as the pots? Thinner tiles will soak up less glaze than a thicker walled pot so cracking / crawling less likely to show on tiles. (If you use 20 epk then the calcined epk would be 16 and I wouldn't add bentonite even then). 

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I deflocculate majolica with a lot of frit. That settles and the deflocculant helps prevent that while glazing. If a glaze is thick, that doesn't mean it needs to be deflocculated. If it is settled with hard layers on the bottom, the yes it need to be deflocculated

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If it is settled with hard layers on the bottom, the yes it need to be deflocculated

Isn't this backwards?  If the glaze hard layers on the bottom, it needs flocculated.

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If it is settled with hard layers on the bottom, the yes it need to be deflocculated

Isn't this backwards?  If the glaze hard layers on the bottom, it needs flocculated.

 

No it isn't. Define deflocculant: an agent that causes deflocculation specifically : a chemical (as sodium carbonate) added to a clay slip to minimize settling out. The same holds true for keeping glaze ingredients suspended.

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Define deflocculant: an agent that causes deflocculation specifically : a chemical (as sodium carbonate) added to a clay slip to minimize settling out

 

An easy way to remember the flocculant causes the molecules to "flock together" and a deflocculant causes the molecules to repel, or become suspended and not to settle.

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Marcia, with all due respect, I think you have it half right. Floc, as you correctly give a good method for remembering, is a flock of sheep that sticks together; defloc is the opposite, the particles repel and separate. However, the flocculated glaze clumps take longer to sink and when they do, they settle in a soft gooey mass that is easy to stir up again. A defloculated glaze settles rapidly and, because typically there is little clay in it, the harder flux and frit materials form an impenetrable layer on the bottom of the bucket. Think of your terra sig recipe. You deflocculate it with soda ash/sodium silicate/Darvan specifically so that the clay particles (which normally would naturally flocculate due to their ionic charge) will separate and then the bigger particles settle out faster leaving the finer particles still floating long enough for you to draw off that part of the liquid as the Tsig.

 

The purpose in deflocculating a clay slip is not to keep the clay suspended, but rather to cause it to separate so that you can add more clay to the same amount of water. It you mix your own casting slip, try it sometime by setting aside the deflocculant(s). The batch will be too stiff to stir when there is still more dry material to put in. Add the deflocs and it instantly turns to runny soup so you can add the rest of the dry clay while remaining pourable. Same with decorative slip - defloc it a bit so you can add more clay to the same amount of water, and then the slip will have less shrinkage/cracking as it dries.

 

With glazes, we come at it from the other direction. We want to maintain a specific ratio of materials to water - get that adjusted first by measuring the specific gravity, but then we can adjust the viscosity of the slurry by flocing or deflocing it. If it settles out too fast, floc it with some saturated epsom salt solution or vinegar. If it is too thick (rare, typically only with recipes high in Gerstley), defloc it with some soda ash.

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Thanks Dick. Mr casey, I stand corrected. Floc and defloc  is my dyslexic brain mixing everything up? So am I floccing when I add darvon to a slip with mason stain or defloccing to keep the stain from settling to the bottom of the slip?

Marcia

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If I add epsom salts to a majolica glaze with settling frit (not clay) . Why does Linda Arbuckle and Rosie Wynkoop and other majolica artists use epsom salts to keep their majolica from settling? I have used it  for majolica suspension as well as to keep my stains from settling in overglaze. Ceramics is full of mysteries! To floc to not to floc! :wacko:

Marcia

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More than Marcia needs, but a more complete explanation for anybody else interested.

 

Epsom salts is a flocculant. If such is a required material in a recipe, it is usually a specified amount dry weight like most other materials. Just include it and it should dissolve by itself during the mixing. If it is needed to correct a problem already in the bucket, it is best to have a small jar of a saturated solution available for administration as needed. To make that, 3/4 fill a small jar (with a tight lid) with hot water. Then put a tablespoon of epsom salts in, cap it and shake until the salts dissolve. Add another tablespoon and shake again. Rinse and repeat with another and another tablespoon of salts until no more will dissolve despite your shaking it. There might even be a few crystals just sitting on the bottom of the jar that just won't go away. Now the water has accepted as much as it can hold, is saturated. Keep it on hand in your fix-it drawer and add a teaspoon at a time to a bucket of glaze that just won't stay suspended (or is already hardpanned as in the beginning of this discussion). There will be an immediate reaction and the watery glaze will become creamy and thicker. Do not add too much epsom salt as it will quickly turn the glaze slurry into glaze Jello. Not good. If this happens, DO NOT add water hoping to thin it back out. That just makes things worse. Instead, reverse the chemical reaction by adding a deflocculant such as a few drops of sodium silicate or a teaspoon of saturated solution of soda ash (made the same way as above, but be absolutely sure you clearly label each jar so you know which is which and use the proper one). An alternative to the epsom salts solution is common white vinegar or very dilute muriatic acid. All are mildly acidic, which is what causes the polarity of the slurry to switch so the particles clump/floc.

 

The opposite is deflocculation, which is accomplished with mildly alkaline solutions, such as sodium silicate or soda ash (notice the common element sodium - alkaline, first column of the periodic table, but we should pull ourselves back out of the chemistry rabbit hole...). Glazes tend to not need deflocculation unless something is really screwed up, like the over-flocculation mentioned above. However, the consistency of clay slips and engobes is adjusted with a deflocculant. A thick slip will instantly turn to soup when a deflocculant is added. Because the nature of the clay particle does not hard pan, a deflocculated slip will settle to a muddy sludge towards the bottom, but then it will stir up again easily.

 

Darvan is a commercial product for similar purposes, works better in certain circumstances, but there are several variants of Darvan so you need to read the label instructions and use the right one for each specific situation.

 

A glaze recipe that has a fair amount of clay content will, for the most part, remain flocculated and only need stirring to keep the slurry consistent throughout the bucket. Recipes that have only a minor amount of clay and are heavy in feldspars or neph sye will have a lot of sodium/potassium in the chemistry. These recipes tend to defloc themselves due to the high alkaline levels of the recipe's native chemistry, and will tend to precipitate and hardpan unless treated with a flocculant. Recipes that have a significant basis of frit usually don't establish a natural level of acidity or alkalinity, they just settle out by gravity. For those you have to flocculate to assist whatever clay is present to clump and hold onto the frit particles. Recipes that are heavy in gerstley borate tend to gel because gerstley is thixatropic (a different chemical discussion but I'll include it here because it is a glaze slurry problem) and this can be ameliorated with a dash of soda ash deflocculant.

 

(And this is just to hold Nerd's horse until he gets here to tell us really what is going on at the electron/proton level...  :P  )

curt likes this

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Dick

Thanks so much for the very clear explanations. (Although the whole subject still makes my head hurt!) 

Just to make sure I understand:  if the problem I have is a "hard pan" at the bottom of my glaze, deflocculation has occurred, correct?   If so, what about adding Bentonite to the recipe?  Is that another solution to the problem?  Or did I dream that?

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Bentonite will work in amounts up to 2%. It is a colloidal clay iirc.

Unfired glazes lacking clay will also powder and rub off pots more easily.

Best solution is to adjust the kaolin(clay) if possible.

Edited by C.Banks

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