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Correct Glaze Specific Gravity

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I understand the need for correct specific Gravity determined by weighing 100ml of the glaze and viscosity determined with a hydrometer. However, I have not found the recommend values for either with glaze recipes. The inclusion of these values with the recipes would be beneficial. Otherwise, the "dip your finger" method of guessing is required for the initial values.

 

I appreciate all comments.

 

Thank you

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Guest JBaymore

A hydrometer does not tell you viscosity.......... it gives you specific gravity by a different method. 

 

Viscometers give you viscosity.  Look up "Zahn's Cup" as one cheap variation of those.

 

At the densities of glazes...... hydrometers are of limited accuracy due to the nature of the slurry.  Pint Weight is more accurate.

 

Proper application consistency varies by the specific glaze and the specific application technique.

 

best,

 

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

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Thank you for the reply. I mis spoke about the hydrometer. I am familiar with the "Cup" method for viscosity. I agree also the consistency varies by glaze. That is the point of my question. Without the suggested SG I do not have a sound basis to determine the correct density.

 

Am I overthinking this and making something simple complex? I am Wayne, Jamie's husband aka the " newly retired M.D.- Glaze maker"

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Guest JBaymore

Thank you for the reply. I mis spoke about the hydrometer. I am familiar with the "Cup" method for viscosity. I agree also the consistency varies by glaze. That is the point of my question. Without the suggested SG I do not have a sound basis to determine the correct density.

 

Am I overthinking this and making something simple complex? I am Wayne, Jamie's husband aka the " newly retired M.D.- Glaze maker"

 

Hi Wayne.  Welcome to the wonderful world of ceramics.

 

Yeah...... you are likely overthinking it a BIT........ but for consistency of end results... the more variables that you can take out of the overall equation...... the more "firsts" come out of that final firing.

 

To determine the "correct" glaze consistency for each glaze she uses...... have her give you the ballpark with the "finger method".  Glaze a bunch of work.  If she likes the application characteristics...... fire the work.  If the fired results are what she wants....... test the S.G. and the viscosity.  Then when you mix new batches.... match to that recorded information.

 

Note that bisque temperature variation can change the way the application works, as can different clay bodies.  So there are a LOT of potential variables.  As an M.D. ......... you have a science background... so I am sure that you are well aware of just how darn MANY of those pesky things are hiding out there waiting to trip up the results. ;)  

 

There is a reason industry uses the standardization and controls that they do :lol: .

 

I agree that the passing around of glaze recipes as we studio artists do leaves a LOT to be desired.  Variables like viscosity, S.G. and exact firing and cooling schedules would be VERY helpful.  But no one seems to do that.  There is a saying in the field :

"Glazes don't travel well."    Water chemistry, slurry consistency, variations in how one applies the glaze, different clay bodies, firing variations all conspire to make duplicating results difficult from one potter's studio to another's.

 

BTW......... With your background....... you likely will LOVE learning to use this software.  Free trial download.  http://digitalfire.com/insight/index.php

 

Enjoy the journey. :)

 

best,

 

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

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I use a hydrometer every week on glaze day-I also use a cup. Knowing the values of each glaze is a learned skill as application of glazes has many variables.

Getting a baseline measurment for me is helpfull but its just a starting point-many cone 10 glazes do have a SG # stated in some books.

I can not address cone 6 as its not my use area.

One last point back in day we all learned this by how it ran off your hand not finger dipped into a bucket of glaze-I still have this skill but as I wear latex gloves glazing I use the hydrometer now.

Mark

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I just ran a batch of glaze tests today with a specific gravity of 142.3. I wrote this into my Excel spreadsheet and if I have a glaze I would like to try in a larger mix I know the s.g., the 100 gram chemicals, and the 90 ml of water I added to the glaze. So I can mix 1,000 dry ingredients and 900 ml of water and be reasonably sure to be close to the original s.g. Of 142.3 and be reasonably sure of having similar results.

 

If you buy commercial dry glazes you might ask the company what their recommendation for s.g. Would be for dipping, spraying, or brushing.

 

i mostly dip and in my very limited experience 1.30 to 1.50 seems to give me good results. I can get a glaze in that area, and it's better for me than sticking my finger in and making a judgement.

 

Plus, doing s.g. with a digital scale and a 100 ml beaker is really easy.

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If your looking for some initial visual benchmarks for the first round of glazes you could use the milk consistency rule of thumb. Brushing resembles whole milk, dipping reduced fat 2% and spraying is 1%. Non fat may be too watery and heavy cream may be too thick. I have been using this to approach with good results. I have however started measuring all of our glazes this week to hone in and establish the re-fill number and test fire to nail down for next time as well as clean up a few that have been on the thick and runny side (meaning way too much shelve grinding and screwed up pot bottoms).

 

I am using a drip tool we had bought a long time ago, and never used, since I couldn't find our hydrometer (don't ask). It actually has been just fine I think. We primarily dip and 19-23 seconds seemed to get me where I wanted to be visually for each of the 30 we have in our lineup (likely about 1.2ish hydrometer reading). I'm going to find that hydrometer and formalize the numbers after testing but the drip gadget seemed to work just fine and if I don't find the hydrometer I might just use it. Each glaze seemed to vary a bit but certainly should be consistent as long as whoever is using it does pretty standard second count.

 

I don't think there really is a standard for anyone to write out on their recipes though. Like John said there are so many variables from your materials sourcing to the firing that it wouldn't mean anything really. Pick a visual benchmark method or stick with the finger method and thin to what you think is right for the kind of application your wife does (thicker for brushes and thinner for dipping) and then take a hydrometer and test and re-test until u nail it. 

 

Make sure when you are first testing for the right consistency that you have your kiln shelves coated with fresh kiln wash and make sure that the test you start with have height and don't go all the way down to allow for some dripping and/or sagging b4 the glaze flows onto the shelve. A standard mark to stop is good aand then you can evaluate if and how much the glaze ran down from being too thick. You didn't mention all your roles but my guess is if you are the new glaze manager then you will likely also be the shelf grinder to remove runny glaze fired into the shelves. If your wife likes to get her glaze line really low on the pot then you are going to need to get this right to the point that the glaze pretty much stays where the original glaze line is before firing.

 

have fun and check out the videos and books offered here on this site.

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I like to put glaze tests on thin slices of insulating brick, just in case the glaze is too runny.

That's a great idea! Not sure why it never occurred to me... Have a bunch of broken pieces of kiln shelves that would work too

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