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Crystalline Glaze Chemistry


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Test Cylinder


While throwing this test cylinder, pull enough extra clay to the top; in order to form the catcher. This cylinder would be inverted on your wheel; with the catcher on top when you finish throwing. You can make them tall and narrow, or wide and short: whatever fits your kiln. As you get your recipe dialed in, get the peak temperature correct, and the flux levels correct: you will find little to no glaze in the catcher.



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"Posted Today, 06:42 PM

"be sure you don't end up, down that burrow, knowing everything about nothing or nothing about everything! "



I woke up about six months ago with exactly those thoughts. " I know a lot about clay and crystalline chemistry, and yet I know nothing."

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It's like soil science.

Chemistry tick

Then ,b. Me there's the soil, temp, weather, etc etc etc so back to "local" knowledge and there are no absolutes esp when humans are involved .

But it is fun, or at least not boring. And humbling when set against the amazingly beautiful pots made by the ancients and the "peasant potters", my term there.

Pres is now trying to replicate his new baby 😊

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Guest JBaymore

...........knowing everything about nothing or nothing about everything!



THAT is when the real journey in your field finally begins.  You are ready to begin to understand.





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Yeh! Knowing that you don't know when perhaps you thought you did!

Someone said to me recently, "you're not Still reading about this stuff....."

Guess I'll never shut the books, no boredom here. And my memory is getting drifty.....sometimes I see a tiny little bit very clearly...then something else changes

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  • 3 months later...

For DW  mainly, and others who fire crystalline.

cone 5 crystalline ( peak 2225f)  total holds(3.5 hours) largest crystal 3"

DW: ten years ago I began to question how much of a roll clay played in crystal development. Six years ago I started doing clay research, one year ago I started developing porcelain  specifically  for crystalline. Pulled this final test out this morning. Looks rather cone 10'ish to me, even though it is cone 5.  PR-2 porcelain. ( and no it is not for sale, nor is this an advertisement.)  think I can stop researching now

the chips on the rim are from my very poor trimming skills..still learning.


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TY LT. Have long felt crystalline could go places, most thought not possible.

DW:  frit 3110.  50%

         A25 silica.  22%

         XL 500 ZNO. 25%

          TiO2.  0.05 %

nerd suspender.  4 %.     Lithium carb. 2.5%.   Nerd no run 0.50% 

fairly simple/ run of the mill crystalline recipe.

DW: will be testing most all the variables over the coming months. Mixed up 200 lbs.



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always viewed crystalline on two planes: the first being it is an ionic bond. (magnetic bond)That said, it also means I believe that the clay body can promote or inhibit crystal growth. The second being amphoretic oxide: which I have not been able to find any supporting data at 2200 (1200C) temps and up. Although crystalline glaze is the only one I know of that can eat threw a 3" brick in a single firing. So I tend to do my experimenting along these two variables.

as a side note, the piece above was fired on the low ramp cycle: still producing large crystals. Next spring I will fire some on the high ramp cycles; which will likely produce crystals in the 4-6" range...although I must say I am very curious to see what molybdenum will do on this clay.

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  • 11 months later...


there has never been a value or ratio for water. You will find a wide variance from potter to potter.

the rule(s) of thumb are:

1. Mix to a heavy cream consistency.  You can thin it down, and simply apply more coats if needed.

2. You will need to add 2-4%  bentonite ( add dry) to help with suspension and slow drying. Wetting bisq helps.

the high % of zinc/frit in the recipe creates rapid drying of the glaze (almost on brush contact) so adjust water until you get comfortable with application. It will crack, do not try to fix it: nature of the beast. As long as it does not flake off- cook it!  Sieving is almost mandatory with this glaze: frit likes to ball up. 

Application of glaze is more relative than the amount of water. This glaze will flow: ALOT!  So application is thinner at the bottom, and heavy at the top of the piece. As a point of reference: 2 coats on the bottom 1/4 to 1/3.  3 coats  on the middle  to the upper 1/3. 4 coats on the upper third.  If you thin it down from a heavy cream then add one coat per section. Dipping does not work well with this glaze.

on page one there is a link showing Adam making and attaching catchers. It is normal for roughly 1/3 of the glaze to run off the pot.

i can post a link showing application techniques if that will help. (DW might have one already?)

there is a steep learning curve with this glaze- give yourself room to make mistakes. You can spot impatient crystalliers anywhere- they are bald!  :)


EDIT: apply piece to catcher before glazing. The less it is handled after glazing- the better.

Edited by glazenerd
Info added.
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I will add to Tom's second sentence - there is a wide variance from potter to potter for many aspects of the tumble down this particular rabbit hole.

I don't use bentonite as a suspension agent, I use a mix of CMC gum in the water - for suspension, as a brushing agent, and to harden the surface of the glaze as I add more coats. The CMC gum mix is about the consistency of heavy cream, and I mix the glaze slurry to the consistency of honey or well-stirred Greek yogurt. And yes, sieving is imperative.

I mix my crystalline glazes in small batches in quart mason jars using an old blender. Hamilton Beach and Oster blender jugs screw onto their respective blade/base with the same thread size as a common mason canning jar. Waring has a different thread size so you can't use a Waring blender; Hamilton Beach or Oster only.  Also get a cheap plastic  funnel for canning to aid in getting the glaze materials into the jar (the bottom of the funnel fits exactly in the top of the jar).



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Many solid-water slurries have a maximum volume percentage of about 60 percent solids.  
Based on that "rule of thumb" in the solid/water slurry engineering domain,  and my experience with slurries both inside and outside of the studio potter discipline I use the following procedure:

for  glazes using clay, crushed rocks (feldspar, limestone, quartz, etc), crushed glass (aka frits),  and colorants as major ingredients :

I start with an amount of water that is 60 of the weight of the solids and additives being used. In other words if the solids is 1000 grams total, I use 600 grams of water.  If the slurry is too stiff, I will carefully add additional water to meet the consistency needed for the application.  When the glaze has been tested and declared successful, the amount of water as a percent of the dry solids is added to the recipe.   I have not needed more than 70 % wt.  water for the glazes I use.   

Most of my glaze application is dipping or pouring.  More water may be needed for spraying.   

The procedure works for me . 


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your question compelled me to a search. Peter Issley (deceased) from the UK wrote a book of crystalline glaze; as did Diane Creber of Canada. Neither of these two address an exact water addition other than "heavy cream" or " double cream." (UK )  

i took a minute to test LT's recommendation: 60% water results in a peanut butter consistency. Crystalline glaze breaks all the fundamental rules of glaze: including water. Using  75% water creates a creamy slurry suitable for single fire application where water absorption is much less than bisq. For bisq, 80% water is a good starting point. 

That said: the suspender I use holds more water than bentonite without gelling. DW uses CMC, which will require a different water level. I know several who use 10% ball clay as suspenders: which  require a different water content. Yellow zinc, white zinc, and calcined zinc all hold water differently. Hence the variables. Most crystalliers have become accustomed to " eyeing"  to their preferred consistency. 

Start with the 60% addition mentioned by LT; then add 10% at a time until it hits a cream consistency you are comfortable working with. The suspender you chose will play a role in that level. 

More importantly: application of glaze as mentioned above. Secondly is application rate: vertical pieces- 0.65 to 0.75 grams per square inch of surface. Flat work: tile, low profile plates- 0.45 grams per square inch. ( application rates are not discussed in books either.) The rim of the plate receives more, and the bottom less: it will flow from the rim to the bottom when it melts.



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  • 2 months later...

This is all so helpful and I'm so grateful for this forum and the FREE information you are sharing with the community. THANK YOU.

After reading about how the key with crystalline is precision, I feel like I already know the answer to this. But before I decide I can't try it in my current situation: Is there any way to create a firing schedule that will grow crystals using a witness cones and a kiln sitter? That's all I'm working with at the moment. 

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thank you and your welcome. Let me qualify my response by saying: I have not personally fired crystalline in a manual kiln. That said: I know many who have and still do. In the many lengthy conversations I have had with manual firers', it requires constant monitoring during the crystal growth ramp holds,  Firing schedules which includes ramping down from peak (cone 6) to growth ramps (cone 04ish) requires keeping a careful kiln log of switch settings, length of time, and kiln chamber "color." Firing manually is not impossible, but it is about as tough as manual firings can get. I can certainly reach out to those who still do for helpful insights, although it might take awhile to get a response. One of our forum members fired crystals manually back in 1973 with good success: perhaps she will chime in. 


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When I first became interested in crystalline glazes (in a school setting where we had digitally controlled kilns) I had only a manual kiln in my home studio. Fortunately my kiln had "infinite switches" that can be dialed up and down as needed rather than single or H/M/L click switches. The infinite switches are critical to be able to tweak the heat input to exactly match heat losses so as to maintain your predetermined temperatures during the crystal growing period. You will also need an external pyrometer and thermocouple (poke the thermocouple through a peephole and pack the space with some ceramic fiber, or drill an appropriate size hole specifically for the thermocouple). As Tom just noted, you must monitor this every few minutes and tweak the switches as neededto be sure the temperature stays where you want it. Finally, manual kilns have kiln sitters which will drop and shut off the kiln due to the heatwork from the extended holds. When the sitter drops, just lift it, push the white button to restart the kiln, and gently rest the weight back down so it sits at a slight angle without triggering the shutoff switch inside the sitter case. It can be done, but it's a lot of tedium.

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