Problems Scaling Glaze Up To Larger Quantity

[algebraist]

If you want to continue reading, the following is an account of what a moron I am.  It turns out that carefully explaining it here led me to figure out my boneheaded maneuver.  Basically I mixed a lot of glaze and it came out all wrong.  One of my speculations below is that maybe my scale is inaccurate at heavier weights.  So after posting this I got the bright idea to test it, and I found a 2kg bag of dog food and brought it into the studio and put it on the scale.  Imagine my surprise when the scale read 4 thousand 4 hundred and something.  It seems I had the scale set to *pounds* and was reading it as grams.  What with old eyes and bits of clay on the display, the decimal point was unnoticeable, as was the "lb" in the corner.  So basically I added a little less than half of every ingredient except water!  Mystery solved.  The good news is that with a little work I can salvage the glaze.  The bad news is that it doesn't change the fact that I'm a moron.  Oh well, you work with what you've got!

 

 

 

The short story is that I just tried to make a 5 gallon batch of a glaze I like, when the largest batch I've made before is about a gallon.  The results are confusing.  The facts:

 

 

1) My basic recipe (which I will include at the end) is for 100 grams, plus an addition of 15 grams of Zircopax and 1.3 grams Veegum CER, for 116.3 grams total.  But I will refer to it hereafter as 100 grams, as one unit of the glaze.

 

2) 30 times this recipe with the addition of 3 quarts of water made just over 1 gallon.  That's what I've been happily using.

 

3) Yesterday I mixed up 120 times the recipe and added 12 quarts (3 gallons) of water.  I used my new Jiffy mixer at the end of a drill, and sieved 3 times (usually I only sieve twice) with an 80 mesh sieve.  

 

 

The surprises:

 

A) The glaze is much thinner (as in less viscous) than usual, and

 

There's a lot less of it than I thought there would be -- it comes up to about 9.5 inches in a 5 gallon bucket (which is about 14.5 inches tall).  Making 4 times the recipe that yielded a little more than a gallon should have yielded more than 4 gallons.

 

 

Here are my speculations:

 

i) Maybe my scale is inaccurate at heavier weights, so that when I was weighing out 2 or 3 kilograms of various ingredients (instead of the usual 1/4 of that amount), it was always giving a higher reading than what was really present.  That would account for the thinness, and maybe also the amount.  In this case I figure I can just let water evaporate until it's the right consistency, and still have a good glaze.

 

ii) I've been using 1.3% "Veegum CER" in all my glazes.  It gives a good consistency and good handling properties.  Probably I could get similar results with bentonite, but I continue to use this because it's been working for me, and I don't want to start a new round of testing to replace something I'm happy with.  But I wonder: Maybe it doesn't scale up nicely, and in larger quantities a higher percentage is needed?  That doesn't really make sense to me, and wouldn't explain the discrepancy in the amount, but seems worth mentioning especially because usually I can mix a glaze one day and all the ingredients stay beautifully suspended for many days, even a week or two.  The batch I mixed yesterday already has the solids all settled out on the bottom.  (Even when I mixed it back up, though, it's still very thin.)

 

iii) I have a new bag of Nepheline Syenite (the one I've had for 15 years having finally run out) from a new supplier.  Maybe there's something going on there.

 

 

I rechecked my method of measuring the water (a line on a gallon jug -- it's right on).  I suppose it's possible that I could have mis-measured some ingredient horribly, but that's not like me and would be a first (as far as I know!).  

 

 

For completeness the glaze is a reformulation of Hesselbeth and Roy's "Majolica" (from "Mastering Cone 6 Glazes") to use the raw materials I happen to keep on hand:

 

Nepheline Syenite:   30.700

Ferro Frit 3195:     14.820

Wollastonite:        21.228

Pioneer Kaolin:      15.621

Silica:              17.623

 

Zircopax:            15.000

Veegum CER:           1.300

 

 

Thanks for any advice.

[Callie Beller Diesel]

Yikes! My sympathies, and thank you for letting the post stand! We have all done things that have required a good facepalm after! (I'll tell you some time about when I wadded a soda kiln, including the posts in sub zero weather without the burners turned on and all the wadding froze...and then thawed. /////_)

I think I'm glad my beam balance is only in metric. This is totally something I'd do otherwise.

[LinR]

I'm sure we all have made stupid mistakes in making up glazes.  I know I have.  Then there is the fun of trying to figure out just what the hell you've done wrong and the duh!  moment when you figure it out.  You are not alone!

Lin

[Mark C.]

Do not feel bad I have made every bone head mistake you can think of in 40 plus years of making glazes-Its not if -its WHEN when it comes to glaze mixing mistakes.

You can fix this very easy many mistakes are not so lucky

The worst ones is when the whole kiln load is glazed and fired and then you find the glaze-been there with the hammer more than once.

[glazenerd]

Alge:

My general rule of thumb about mistakes is: once I cannot count them on both hands, I stop counting.

Nerd

[oldlady]

i know you educated potters list the kinds of ingredients together in groups, glass formers, melters, etc.  i found that the only way to make glazes work is to list the ingredients by weight from the smallest to the largest.  that came about after i found the 1000 gram weight still on the scale after 4 more ingredients past the huge amount of whatever it was. now i don't put the heavy weight on until the end.

[Denice]

That's a great tip on the scale weights,  I could have used it when I was using a Ohaus scale.  I am using digital now, the magnet  gave out according to the Ohaus company and it would cost me as much to get it fixed  as to buy a new one.   Denice

[Mark C.]

Digital scale is the way to go-I leaned about them on this site and have two now-they are so much quicker than my triple beam(I still use that for small test batches like 500 grams)

You can get them at amazon for under 20$