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Supersaturated Solutions And Crystal Formation

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I was watching a video about making your own "magic rocks."  I remember making a magic rock garden when I was a kid.  Basically the rocks are metal salts suspended in a sodium silicate solution.  Metal silicate crystals form.  I hope everyone remembers making rock gardens.

 

This got me thinking about saturated solutions and crystal formation.  Let's say i made up a supersaturated solution of a metal salt, for example copper sulfate, then placed a bisqued  pot into the solution.  The pot would take up water and crystals would form on the outside and possibly in the clay body of the pot.  I could remove the pot, let it dry, then spray a coat of glaze over the newly formed crystals.  I could do this with Zinc, Boran, Molybdenum, Iron,  or Lithium salts.

 

Many people soak pots in saltwater or K salt solutions prior to firing. But how about soaking the pots in Metal salts too... I think i will give it a try.   I might get some cool glaze effects when the crystals interact with the glaze.

 

I could even add metal salts to a  clay body, then spray a concentrated solution of Sodium silicate over the pot and fire it.  It may develop "ceramic rock garden effects."

 

Jed

Biglou13 likes this

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what ever you do be careful. Last time I read up on anything to do with metal salts they were said to be pretty nasty when it comes to health hazards.

 

Yup.... get MSDSs for them before you start to play.

 

best,

 

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

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The copper sulfate will decompose into blackcopper oxide and  release acidic sulfer compounds that will probably degrade your bisk ware and completly discolor your glazes. There will be no crystals left past 300 degrees F and it will decompose at around 600 degree F.

 

Most water soluable metal salts dont hold up at high temperatures. That is why they are used in pit fires and sagger fires. They just degrade to the oxide.

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They just degrade to the oxide.

 

Yup.

 

Deciding what to test and what might not be worth it is where an understanding of glaze chemistry comes in.  (Chemistry in general, actually.) 

 

But sometimes the best teacher, particularly for visual learners, is concrete experience. 

 

And sometimes,...... sometimes................ we stumble on something that not supposed to act the way it does... and we find nice surprises.  (This usually means that there is a variable in there somewhere that we are not controlling. ;) )

 

best,

 

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

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I'm still very new to this and make many mistakes. I assumed the metal crystal would decompose, leaving its oxide. My question really is what type of effect one would obtain when the local oxides interacted with the glaze. Would it only cause local or widespread discoloation? Would there be a color gradient surrounding each crystal? A "sunburst effect".....

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The point here is that you won't HAVE crystals at the point where anything is reacting as far as the developing glazes go. You'll simply have concentrations of the oxide wher the crystals once were (for the exampele... copper oxide). Not much different from using copper oxide to start with and maybe using a toothbrush to spatter the oxide solution or something like that.

 

You CAN get some intereting "watercolor" type painterly effects out of soluble colorants by painting solutions on top of a dry glaze powder ..... not what you are thinking here... but one proven use of the solubles.

 

Your original description of the rock candy process is exactly whay is happening in many glazes as the kiln cools after the glaze melts. It is the super-saturation of certain oxides in the liquid glaze melt that are then percipitating out onto the glaze surface (and sometimes within the layer of glaze) that give great interest to some types of glazes. macro-crystalline glazes are an extreme example of this idea.

 

best,

 

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

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The following article sent me down my misguided path.  It is really cool by john Britt, on e of my heroes.

 

www.ceramicstoday.com/articles/flambe_magic.htm   Take a look at this. it is really cool.  I will try to follow the instructions here to get the crystals to form in the glaze as he noticed.

 

Jed

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Here is the key line there: "Crystals will also form if glaze slurries containing soluble materials are allowed to dry out completely."

 

What then happens to that "crystal" as the kiln heat up is that whatever chemicals it contains are now concentrated in one small spot, rather than distributed throughout the glaze as normally would be the case. As the kiln heats up, and in the presce of oxygen, all of the materials in that crystal that CAN be changed into an oxide form will do so. No longe that crystal.... but just a concentration of oxides that were composed / selected by the crystal formation process.

 

Glazes are mixtures of the oxides of metals and metallic earths (definition of ceramics there). So the oxides in that small location of the glaze where the crystal was are now different than the oxides in the "background" glaze. So the visual characteristics in that small spot will likely be different than what is happening in the background.

 

Bingo.

 

best,

 

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

 

PS: I've had greeat luck with deliberatley freezing glazes to do this.

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In the end, the crystal material has to bond with the silica. The crystal salts can also be looked at as fluxes to the glaze. Lithium, boron, calcium, etc will form crystals on evaporation  and precipitation  in the glaze. I believe that's what John Britt saw in his test.

 

Titanium can form crystals in certain glazes as well, but most glazes that have crystal growth need a time/ temperature sweet spot to allow for that growth.

At least these have been some of my observations.

Wyndham

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There is a difference in this crystal discussion between the crystallization of SOLUBLE RAW MATERIALS in the wet glaze slurry (which is what John's Britt's article is talking about there) and the creation of crystals in the cooling glaze MELT. Two different beasts.

 

best,

 

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

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One way you might get a psudo-crystal look with a glaze is to imbed crystals in the surface of the leather hard raw clay. Use somthing that would burn away in the bisque like large sugar sprinkles. Once they were burnt away you would have a surface with crystal like impressions that you could glaze over.

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John,the reference to both Wet crystal formation and the silica metal bond to grow crystals was to point out the 2 different and distinct paths of what a crystal is. Sorry if I did not make that point clear.

My copper red uses both frit 3134 & Gertsly Borate and if left open to the air, an evaporate crust forms on the side of the bucket. Another glaze, if forget which at the moment, will develop a crusty crystal over the winter in the closed bucket, much the same way any crystal forms due to a super saturated solution cooling and giving up crystals.

 

As both you and Bob have said that these WET crystal are not going to last out of their environment that produced them.

 

Back in the 1920's to 40's soluble salts were used in glazes and were erratic in some cases because of the solubility problems.

 

Just clearing up my obscure post,

Wyndham

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John,the reference to both Wet crystal formation and the silica metal bond to grow crystals was to point out the 2 different and distinct paths of what a crystal is. Sorry if I did not make that point clear.

That was why I posted what I did... for other readers.

 

best,

 

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

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