A journey...

[John Saare]

A journey of a thousand blogs..., uh..., begins with a blog, though I suppose this is really more of a test drive ;).

I'm finally getting around to experimenting with glazes a bit..., moving beyond the recipes provided by my instructor.

I've been looking forward to this a long time..., anticipating it.  So naturally...

When came the time to combine the dry with the wet..., what do I do?

I invert the proportion of glaze materials to water..., so end up with 4 times the pre-sieve water I would ordinarily start with.

Sigh.  

Have placed a screen over the bucket (to keep the critters and what-all out)..., and suspect it will be quite awhile before settling/separation and evaporation bring the SG up to something more like what I want.

Luckily..., have other glazes that need mixing..., so hopefully I've learned a lesson.

[John Saare]

OK..., if there's an exothermic thing going on, I'm assuming that the quantities involved keep temps in a safe zone. Heh, FWIW, I've ordered the calcium chloride, so will have that on hand..., but it looks like the glaze is settling out sufficiently to permit removal of a good part of, if not most of the excess water. We shall see. FWIW..., this is a batch of the "Raspberry" from Mastering Cone 6...

..., I wonder if there's a "Chemistry for Dummies" on Amazon... ;)   Why yes..., yes there is!

[Norm Stuart]

John - It takes 68 grams of calcium chloride to counteract 100 grams of Darvan 811.

It takes 74 grams of magnesium sulfate to counter the same 100 grams of Darvan 811, because a mole of magnesium sulfate weighs about 8% more than a mole of calcium chloride.

Just from experience we're talking about a teaspoon or two for your 2,000 gram batch. It depends on how "hard" your water is.  The more calcium and or magnesium dissolved in your water the harder it is and the more it suspends clay particles.

My math assumes the Darvan 811 (sodium polyacrylate) is 42.5% water as it ships from Laguna Clay and the calcium chloride is dry. Darvan does not tolerate being frozen and thawed and does decompose slowly over time.

If left open Calcium chloride absorbs moisture from the air and gives off heat, which is why it's sprinkled onto sidewalks to melt ice.

After mixing Darvan with calcium chloride, you end up with sodium chloride (salt) most of which pours off with the excess liquid and the strands of Darvan pladtic bound to calcium, some of which will pour off with the excess liquid.

[John Saare]

..., forgot to mention..., it's a 2000g batch

[John Saare]

Alrighty. My understanding is that very little darvan is required..., by volume..., is the usage of the calcium chloride similar?

[Norm Stuart]

All of these items are just 2 days from being in your studio with Amazon.com or eBay. Stuff there is typically 1/3 the price at a pharmacy.

Amazon Calcium Chloride "Ice Melt"  25 lbs for $12.18

eBay Ammonium Sulfate 5 lbs for $14

Magnesium Sulfate 2 lbs $8.99

Darvan is essentially a water softener and the calcium, magnesium and ammonium sulfate add back the hard water minerals which make the water hard agin and float the glaze particles.

Darvan-811 is the specially polymers which changes magnesium and calcium for water treatment and pottery use, Sodium silicate is a poor substitute.

[John Saare]

Thx Norm! I might actually have some darvan..., though nothing of the flocculants..., next trip to Creative Ceramics in Santa Rosa and I'll remedy that. Sigh..., chemistry was the one subject I somehow missed..., definitely regretting it!

[Norm Stuart]

Mix in a defloculant like Darvan and the solids should settle out overnight. Pour out the excess water and stir in a flocculant like calcium chloride or magnesium sulfate or ammonium sulfate to resuspend the glaze to prevent it from hard panning.

The deflicculant binds to calcium and magnesium ions, releasing sodium in their place. Most of the sodium ions are poured out with the excess water.  Chemistry beats brute force.

[John Saare]

Heh..., just wondered if I could centrifuge the bucket (2 ga.)..., slowly and carefully..., on my wheel...