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Bluegeckopottery

Glaze to thick or to thin

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I'm not super picky about the viscosity of the glazes in my studio. I check them regularly to make sure they're not too thick, but I do not use a hydrometer because I do not have the time to deal with it, and have not found it to be necessary. I eyeball them to a creamy chocolate milk consistency. My students are instructed to dip their pots for a count of 6 to get the glaze the right thickness. Our count is a little fase than seconds, but about 5 seconds would be close. As they learn to use the glazes they will often go a little thicker to get them to run more, but the 6 count provides a consistent baseline from which to experiment. For the second dip, they do a 4 count. No more than a total of 12 is allowed, or the glaze will be too thick and either start to crack and flake before firing, or run too much in the firing.

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I use my eye and if the glaze seems like single cream then it's usually ok. Not very scientific I know but you get to know our glazes the more you use them. Try doing a series of test pieces and keep a note of the consistency of them. Failing that I saw there was a dvd available on the 4th May ceramic daily site which seemed foolproof.

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I use a DuPont viscosity checking cup. Basically I just time how long till the ladle full of glaze runs through it. My glaze is very picky and I have to get it withing a second of my preferred 19 second range.

 

You can make a home made one pretty easy once you have a good batch to refer to.

 

here is the tool I use

0000102_300.jpg

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Viscosity cups will measure viscosity which is not the same as specific gravity though it can be a very important factor in how a glaze behaves during application.

 

Here's how I measure specific gravity.

I bought a cheap plastic 100ml graduated cylinder on the 'net. It was like $3US.

put the dry, empty cylinder on your triple beam balance and zero the balance.

Stir your glaze and pour 100ml into the cylinder then weigh on your triple beam balance.

Should weigh something MORE than 100 grams since 100 ml water = 100 grams

if it weighs 150 grams then the SG(specific gravity) is 1.50

 

Most of my cone ten glazes work best between 1.35 and 1.50 SG but so much depends on how your whole process. Each clay and glaze will be a little different. Heck individual shapes of pots make require some added water to keep the glaze from going on too thick. You'll have to figure out what SG works for your glazes/ware BUT this method will get you a repeatable starting point.

 

If you want to get even more since lab-ish, do this. Make some test tiles and get a quart of your glaze. Measure the SG of your quart then Let the glaze settle out and pour off some of the water (keep it).

Now measure the SG. Dip a tile. Mark the Sg on the tile. add some water, measure SG, dip and mark the tile etc etc etc until you have added all your water back in.

Fire the tiles and then you'll have lots of info for THAT glaze. It may look better thin on one clay and thick on another.

Hope this helps!

NOW, go make some test tiles!

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Speaking of dipping.... I just bought Duncan's Pure Brilliance dipping clear. Used a viscosity cup and added water to get it to 25. When I remove my dipped piece from the bucket, their were lots of little pinholes where the glaze did not stick. (This is before firing). Did I get to many air bubbles in my glaze before I dipped? I used a drill with a paint mixer. How do I fix the piece? blink.gif

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Speaking of dipping.... I just bought Duncan's Pure Brilliance dipping clear. Used a viscosity cup and added water to get it to 25. When I remove my dipped piece from the bucket, their were lots of little pinholes where the glaze did not stick. (This is before firing). Did I get to many air bubbles in my glaze before I dipped? I used a drill with a paint mixer. How do I fix the piece? blink.gif

 

 

Mixer was fine-just wait a few minutes next time and use a stick for final stiring.

As far as the tiny bubbles-when the glaze dries just rub them out with your hand carefully then fire the piece..

Mark

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Buy a glaze hydrometer and you will never have this issue again.Its a glass tube about a foot long with graduations on the inside.

Mark

 

 

 

Mark:

 

Different glazes are optimum at different viscosity levels, using a hydrometer how do you utilize it to measure the correct viscosity of say a copper red versus a matt white? I agree that a hydrometer is an easy and efficient method, I have just never understood how you determine the correct level for each glaze.

 

As always, thanks for sharing your expertise.

 

 

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Guest JBaymore

In my experience, viscosity is a much more important property of glaze slurries than the specific gravity. It tells more abnout how the slurry will actually apply. It combines the issue of specific gravity with that of rheology. Industry relies heavily on viscosity.

 

Also at the typical SGs of glaze slurries, it is my understanding that the standard hydrometers lose their accuracy.

 

best,

 

..........................john

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Guest JBaymore

Different glazes are optimum at different viscosity levels, using a hydrometer how do you utilize it to measure the correct viscosity of say a copper red versus a matt white? I agree that a hydrometer is an easy and efficient method, I have just never understood how you determine the correct level for each glaze.

 

Through testing with the specific glazes. You mix glazes to different test values (either SG or Viscosity or ????) and then apply the glazes in a highly standardized way to the actual clay bodies that you are going to use. Record the tests, record the results. Decide which mix works the way you want.

 

best,

 

.......................john

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I agree about the various ways to measure the right water content. I use viscosity for all slip measuring and thats works well for me. I learned the hydrometer for glazes and am dialed in with it now after all these years-I do use a new one every 5-10 years as I break them now and again-I could learn viscosity for glazes but if its not broke I'm not fixing it.

I have learned the various reading for most of my glazes simply by testing trail and error. I write the measurement on the side of bucket. Some glazes are very touchy others not so much.

I originally learned this by how it ran of my hand-(back in early 70's) and since mid late 80's I always wear latex gloves when glazing so thats not an option anymore.

Most of my glazes run around the 1500 -1550 mark on one of the scales. I made a plastic tube so I can measure smaller amounts as well.If I can I'll take a photo and post a new thread on this.

Big shows coming up soon spare time is short.

Mark

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We have something like 17 glazes in use at any one time. They vary considerably in their behavior/rheology. I've found that no one method works. The problem with the hydrometer and viscometer (cup with a hole in the bottom style) is that the viscosity of the glazes covers a pretty wide range. We have a very viscous glaze that a hydrometer won't move in, and it heaps up so bad that you can't use the 100ml trick to get the specific gravity. We have another glaze that is, I'm guessing, so thixotropic that when you dip a series of smaller objects in it, the stuff won't stop sloshing and it's hard to get a level line (one color top, another bottom, example). There is a lot to be said for testing glazes and matching that to visual/physical observations, along with measurements.

 

Joel.

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I agree about the various ways to measure the right water content. I use viscosity for all slip measuring and thats works well for me. I learned the hydrometer for glazes and am dialed in with it now after all these years-I do use a new one every 5-10 years as I break them now and again-I could learn viscosity for glazes but if its not broke I'm not fixing it.

I have learned the various reading for most of my glazes simply by testing trail and error. I write the measurement on the side of bucket. Some glazes are very touchy others not so much.

I originally learned this by how it ran of my hand-(back in early 70's) and since mid late 80's I always wear latex gloves when glazing so thats not an option anymore.But I can stll do this as its like riding a bike years later.

Most of my glazes run around the 1500 -1550 mark on one of the scales. I made a plastic tube so I can measure smaller amounts as well.If I can I'll take a photo and post a new thread on this.

Big shows coming up soon spare time is short.

Mark

 

Sorry i hit the wrong button while in edit mode

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Sorry to re-vitalise an old thread but I find this Glaze world very much like magic, even when science is applied. So being new to the world and alone in my testing I must reach out for knowledge.

Specific Gravity makes 100% sense to me and in my head it is straight forward. 

 

My question is thus.

Would it stand to reason that a glaze with less materials in its mix will weigh less then one with a larger selection.

for example: will a clear be lower in specific gravity then one with colours in it.

-----

This is my first attempt at making a glaze and for clarity I am not the potter in the family, this would be my wife. She has always purchased ready made slips and clears, and when I asked her why she never after all these years (30 years as a potter) she has never made her own glazes, I was told that it was a massive confusion for her and she has concerns about the mad science chemicals being used. 

 

I have spent a year building her new studio and during the processes I started imagineering how this is done in my head. Now that the play house is built Id like to make glazes for her. 

Now here we are 5.5 litre batch of way  (in my opinion) to runny Clear.

----

My base is from a recipe passed to her from an old friend. The first column is what I was given the second is how i applied it based on reading and trying to understand how to apply the math.

  • Bentonite 1  |  for 5.5 l i used 010grams
  • EPK 27.5     |  for 5.5 l i used 275grams
  • FLINT 27.0  |  for 5.5 l i used 270grams
  • Frit 44.5       |  for 5.5 l i used 445grams
  • Total 100     |  Totalling 1000 (5.5 litres / 1.5 gallons)

So the math came from trying to understand the way these things are combined. Seeing it from outside the club is rather like reading a magic spell! Finally I found a post within this forum that seemed straight forward,  but in practice the end result seems to me to be incorrect as it is to runny / thin.

To make a batch recipe
Simply forget that it is percentages and think of them as just numbers. Then you can treat each number as any unit of weight you want to use - grams, pounds, tons, doesn't matter so long as you use the same unit for the whole batch. If you use the numbers as is, you might have a 100 gram batch, a 100 pound batch, or a 100 ton batch (though that would be a pretty big batch...). If you need your batch to be a different size, simply multiply every number by the same multiplier.

  • 100 gram batch makes about 1/2 cup of glaze or enough for a small piece or test.

  • 1000 gram batch makes enough for a 1.5 gallon ice cream tub, so multiply all the numbers in the recipe by 10.

  • 5000 gram batch will make about a half-full five-gallon bucket of glaze, for which you would multiply all the numbers by 50.

A "mathematical safety" hint - after you have multiplied each number by 50 (or whatever), add up all the new multiplied numbers to make sure they now add up to 5000.
 
100 x 50 = 5000 (5000 is how much water in use) each individual ingredient added together must also equal 5000

I know i have applied my reading incorrectly and am once again on the hunt for a way that I will understand clearly enough to be a success.

 

To apply the specific gravity math what should this way?

----

Any takers?

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arggg, just had my post deleted when I tried to post it. i'll try again

 

"Would it stand to reason that a glaze with less materials in its mix will weigh less then one with a larger selection.

for example: will a clear be lower in specific gravity then one with colours in it."

 

maybe yes, maybe no but doesn't come into it that I can think of

 

  • Bentonite 1  |  for 5.5 l i used 010grams
  • EPK 27.5     |  for 5.5 l i used 275grams
  • FLINT 27.0  |  for 5.5 l i used 270grams
  • Frit 44.5       |  for 5.5 l i used 445grams
  • Total 100     |  Totalling 1000 (5.5 litres / 1.5 gallons)

Bit of an oopsies with your math re measuring the water. Total dry ingredients equals 1000. Usually add about 70-100% by weight of water to that. 

So, just for the sake of argument say 70% therefore 1000grams + 700 grams = 700 ml. 

I would try it with this amount, test the sg (for reference), dip a test tile with 1,2 and 3 dips then add another 100 grams and repeat tests then once more with another 100 grams of water.  Can't comment on the glaze as don't know which frit you are using. (might want to up the bentonite to 2 and if the glaze still settles out quickly add a titch of epsom salts solution). I like using 100 to 200 gram batches for testing. Keep good notes  :)

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How much water a glaze needs in order to be the proper viscosity for dipping will depend on what's in the glaze. Glazes that are high in EPK or feldspars or iron oxide will require more water than those that are low in those ingredients and high in materials like flint or frits.

 

Some colorants are very light and fluffy, some are very heavy. Same goes for the materials in the base formula.

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Bit of an oopsies with your math re measuring the water. Total dry ingredients equals 1000. Usually add about 70-100% by weight of water to that. 

So, just for the sake of argument say 70% therefore 1000grams + 700 grams = 700 ml. 

I would try it with this amount, test the sg (for reference), dip a test tile with 1,2 and 3 dips then add another 100 grams and repeat tests then once more with another 100 grams of water.  Can't comment on the glaze as don't know which frit you are using. (might want to up the bentonite to 2 and if the glaze still settles out quickly add a titch of epsom salts solution). I like using 100 to 200 gram batches for testing. Keep good notes  :)

 Thanks for this info

Up until 5 mins ago i was reading info that stated your information almost word for word. I like that sort of synergy as it tells me there is fact to the information being disseminate through out the web.

I'll let it settle out and gently pull about 4 litres or water off of the top. Ill weigh it out too, so I know ruffly whats left.

 

I have also read that I should be seeing about 145 grams specific gravity for a clear glaze. Right now it is sitting around 120, how does that sit with you all?

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