[yedrow]

Is there a rule of thumb calculation for the ratio of water to chemicals in a glaze slurry, assuming a target specific gravity? This is probably easier than I'm making it but it's late and I'd like a short cut. Note, I'm assuming that sg and material volume are different because of the relationship of flocculated/deflocculated clay to water.


Joel.

[Mark C.]

If there is I would like to know it. I mix up a few 5 gallon buckets of glaze each week and always adjust the SG the next day by adding more water or taking some off. For example as I just did this this evening-mixed two buckets and mixed one a tad thin so I put a stick across the bucket which tells me to remove some water when settled in am. Monday is glaze day this week for me. The other glaze was mixed thick and needs an adjustment of more water is am.

When I was mixing tons of slip years ago(slip business) I had a dry material to water formula like you are asking about as it was always the same.
As for glazes I have always adjusted them each time-Maybe I should revisit this as I do mix many glazes over and over say for 35 years almost every week for 10 months.
This may be a forest thru the trees moment for me-I do know they vary enough to need different amounts of water per glaze.
thanks.
Mark

[yedrow]

They vary a remarkable range from what I've seen. A copper red glaze or magic black goes on very thick and in the slurry has a sg of perhaps 160, or even 170. The yellow salt glaze though is extremely thin, but its sg is like 150 I think. My cone 6 glaze is thicker than the yellow salt with an sg of 135.

All of this must involve a relationship between clay (our suspenders) and the water, as well of the percentage of water in the slurry. I sure would like to know that a general rule for that relationship. For instance, if it has X bentonite, or X ball clay it will perform differently than with no bentonite or 1/2 X ball clay.

Right now I need to add 1 percent cobalt oxide to 5 kg of slurry. I'm really not wanting to have to mixa dry mix to do this, Yes, it is laziness mostly.

Joel.

[Wahine]

Mark, do the glaze makers tell you what the sp of each glaze should be, or is this something you have to figure out on your own? I'm mixing some dry glaze ingredients for the first time. I cannot see the 'fun' that others see in it. Totaly drudgery for me, way to much like cooking.

-chantay

[Mark C.]

Wahine, on 22 October 2012 - 11:21 AM, said:

Mark, do the glaze makers tell you what the sp of each glaze should be, or is this something you have to figure out on your own? I'm mixing some dry glaze ingredients for the first time. I cannot see the 'fun' that others see in it. Totaly drudgery for me, way to much like cooking.

-chantay

I'm not sure what glaze makers you speak as I'm the glaze maker and am making all my own from scratch some are my own formulas.
I learned what sp each glaze each works best by testing-lots of testing .This has taken many firings over many years.I'm working in porcelain so that sp is for this clay at cone 11. After almost 40 years one also has a feel for this
That is the only way to get a good sp with homemade glazes I know of.

As far as making glazes it a means to get to the end-that is the way for many processes in ceramics weather making clay from scratch or glazes or kiln building its part of the final finished ware we all like at the end of the line. We all have our favorite parts -some like to form some like to fire some like other parts-I like to glaze pots and fire for example but after glazing 10 hours and loading 2 glaze kilns today I'm a bit beat and it feels like work and my body says it was a hard job. But I still like it as its part of the process and no matter what I like or do not in ceramics its all part of the whole. I learned long ago that trying to master all the parts is the key. It takes discipline and focus not easy points in todays world.
making glaze that works great and customers comment on it at every show is very rewarding. I focus on that when mixing glaze-I always mix the day before needing it as well.
I'm not big on cooking but I like to eat and cooking gets me there so I cook-its just like that.

One last point is that people pay me to work in the studio by buying my wares-Its still amazing after almost 40 years-to be able to carve out my own life doing what i want to do.
Glaze making is just a part of that life.
Mark

[JBaymore]

yedrow, on 22 October 2012 - 11:09 AM, said:

They vary a remarkable range from what I've seen. A copper red glaze or magic black goes on very thick and in the slurry has a sg of perhaps 160, or even 170. The yellow salt glaze though is extremely thin, but its sg is like 150 I think. My cone 6 glaze is thicker than the yellow salt with an sg of 135.

All of this must involve a relationship between clay (our suspenders) and the water, as well of the percentage of water in the slurry.

Joel,

This is why I've said before that the rheology (flow characteristics) of the glaze is more importqant than the specific gravity. And why a viscometer is the tool to use to match one batch to the next, not a hydrometer.

And you can pretty much standardize the content for a single glaze, batch to batch (unless one of the matterials analysis changes). But there is no "rule" that I know of that applies to all glazes.

best,


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

[neilestrick]

Each glaze will require a specific amount of water to achieve a certain viscosity or SG. Generally speaking, the higher the clay content in the glaze the more water it requires. I have glazes that I can fit 10,000 grams of in a bucket, and others that will only fit 8,000 grams. There is no standard viscosity or SG that is universally used, as each person has their own preferred consistency. In my studio I mix them up so that a 6 count in the bucket is the proper thickness of glaze. I know other studios that mix them much thicker and dip for a shorter count. Brushing glazes are totally different, and can also be watered down as needed. I do not use a viscometer or hydrometer. With 15 buckets of glaze that often sit open for hours at a time, I would spend all my time testing and adjusting them. I just eyeball it, going for a creamy chocolate milk consistency.

[yedrow]

Thanks everyone. I'm piecing this stuff together in my head, bit by bit. I'm going to have to be as patient with glazes as I have been with throwing pots, not an easy task for an impatient man, lol. One of the two glazes is responding to deflocculation, and one isn't, which is pretty interesting; especially since I at least have now gotten a glaze to respond to deflocculation. So, back to the books to reexamine the relationship between clay and the glaze slurry.

Joel.

[Ben]

look up broginarts formula
I have it in a spreadsheet if you want it.

Be careful deflocculating a glaze. It will settle out into a rock in the bottom of the bucket if you go too far.

Ben

[Wahine]

Thanks for your reply Mark, I was thinking of premade glazes, wet or dry. Yes, test, test, test. I think what you said, " I learned long ago that trying to master all the parts is the key," is one of the reason pottery sings for me. I have done art for 30+ years, painting mostly. It was very tedious at times, the same thing day in and day out. With pottery, each day can be a day to learn or try something new.

Neil, are you talking about one of those slotted sticks that painters use? Sounds like a simple yet effective method. I think the whole point is consistant results, right?

-chantay

[Dinah]

Ben is spot on here. Go to the appendices of Hamer and Hamer's The Potter's Dictionary. And BTW it's Brongniart's Formula. Wonderful reference. Every pottery should have one.

If one is using commercially pre mixed/made up glazes, then you'll have to test, and determine thickness for your firing schedule, and your body. None of us on these forums can predict your outcomes to your satisfaction. And that's a given. I'm not a user of commercially prepared glazes mixes, but correct me if I'm wrong - don't these mixes usually come with some ball park mixing instructions to facilitate ease of use and application?

Another idea is to find someone in your area who has some experience and ask them to pop over and give a look-see to what's going on. Another thought in these days of uploading videos from smart phones, etc., you might be able to cadge a quick seminar if you made a video of how the glaze looks when poured from a ladle from a height, and pouring off your hand after you've submerged it. I have to say in the interest of strict health and safety, wear a vinyl glove in case of open cuts. I don't, but that's my choice.

Here's a thought for this forum: encourage more intelligent discussion by having the capability of posting a video from members to solicit assistance because so much of what we do and wish assistance for is based upon visual analysis. However, given some of the glitchy stuff I just experienced signing on 20 minutes ago, maybe we are a little ways off from this type of technology.

Comment if you think it would help you!

[Idaho Potter]

Commercial glazes are sometimes a bit touchy. I have one that I've used for several years successfully, so decided to make it my basic white (Snowflake White) and bought 25 lbs. dry and mixed it up as I'd done the smaller batches (12 oz. water per pound of dry). Much to my dismay--although it looked the same as the smaller batch--it ran like a sonofagun. I've spent the better part of a week trying to grind the mess off the shelves. Totally ruined a half-shelf that I now have to replace. I've written to the manufacturer but haven't heard back as yet. It may be a bad batch, but I don't have a clue how to fix the problem (there may not be a fix). It's like piling up some money and setting fire to it.

[Ben]

Idaho Potter, on 04 November 2012 - 06:45 PM, said:

Commercial glazes are sometimes a bit touchy. I have one that I've used for several years successfully, so decided to make it my basic white (Snowflake White) and bought 25 lbs. dry and mixed it up as I'd done the smaller batches (12 oz. water per pound of dry). Much to my dismay--although it looked the same as the smaller batch--it ran like a sonofagun. I've spent the better part of a week trying to grind the mess off the shelves. Totally ruined a half-shelf that I now have to replace. I've written to the manufacturer but haven't heard back as yet. It may be a bad batch, but I don't have a clue how to fix the problem (there may not be a fix). It's like piling up some money and setting fire to it.

Sorry to hear about this.
Best course of action in future will be to test all new ingredients/glazes. If you buy a new bag of a chemical, make a small batch of glaze with that chemical from the new bag and test fire it. Same for new premixed glazes.
Make up some test tiles or save those pieces that don't survive the bisque and before using an untested batch of clay or glaze, fire a test tile sitting in a saucer of known good clay to catch any drips.
takes some planning ahead but solves more problems than it creates.

Good luck,
Ben