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JessHobbyPotter

My first kiln load with 3 macro crystal glazes

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Thank you to everyone who has been so helpful so far.  I programmed my first kiln with a schedule I modified from the Plainsman Schedule I found online and combined with William Schram's.  They were really close and so I considered that 2 votes in its favor.  I had 11 pieces in the kiln, and three different base glazes (A Version of Snair's Metallic macro crystal, Tin Foil II, and Turnidge MFE) and within that there were color variations with (NiCo3, CuCO3, MnO2+CoO, TiO2+CoO+MnO2, NiCO3+CoO+CuCO3)

About 1/2 grew macro crystals, and 1/2 came out matte.  My favorite was the Turnidge MFE +TiO2+CoO+MnO2 (I hoped it would be purple on tan, but it was mode periwinkle with tan and a dark indigo pool) . I love the variety of the crystal shapes, but I expected rings from the ions and holds in the firing schedule.  I have to read more on that.  

and the Turnidge MFE + NiCO3+CoO+CuCO3 which i thought would be blue on green, and it kinda was.  The brown clay is just what was there.  I will try these again with white clay.

I have only attached pictures of my two favorites.  I can put pictures of the duds too... but right now i am happy that I got 2 that I really like.

1908261903A1.jpg

1908261903A1a.jpg

190826smGr1903B1.jpg

190826smGr1903B1b.jpg

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Very cool, you can try soaking overnight in a dilute acid solution to see if it brings out the crystals better.  Do it with a test piece though, don't want you to experiment with something precious

Edited by liambesaw

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I am thinking about re-firing the pieces i don't like...  you know, since i don't like them.  I have been reading and suspect that the ones that didn't grow macro crystals may have needed a longer soak.  I also want to go back to my pictures and see if they all happened to be on the same shelf or the same side of the kiln.  Maybe add another layer of glaze at the top to see if i can get something interesting to happen.  Below are two of the "dud"s.

dud2.jpg

dud1.jpg

Edited by JessHobbyPotter

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Kiln 2 with a different schedule (unfortunately before I saw Glazenerd's advice about reducing the temp in the first schedule a bit).   First, here are the 2 duds from before.  I added more glaze and refired.  The third is my favorite glaze from last time on white clay instead of brown. Apparently this will be three separate replies.  Sigh.

refired dud1.jpg

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dud 1: first time it was Shimbo's Tin Foil II base glaze with no colorants.  This time I added cobalt 008 on the rim and Turnidge MFE with no colorants... just the cobalt on the rim.

dud 2: first was Shimbo's Tin Foil II base glaze with CuCo3. This time I added Turnidge MFE with no colorants.

refired dud 2.jpg

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Jess: going to turn your results into an educational dissection of results. 

On 8/26/2019 at 8:50 AM, JessHobbyPotter said:

Your initial results are not that far off the mark. This glaze will pool, or run off when fired to peak- normal. The question then becomes: is pooling or run off excessive? In this case your peak firing temp is 15-20F to high. You have a complete melt, no visible grit or unincorporated particles of dolomite or tin.  Next issue is crystal population? If you like it- do nothing. Crystals growing on top of each other is nothing new: but when it gets excessive it hinders crystal growth. Drop zinc from 25% to 24.75% to start and simply add 0.25% into the silica %. Check your next firing- happy? Then onward.

1908261903A1.jpg

1908261903A1a.jpg

Now to look at the actual ramp holds that grow crystals. The recipe is reactive: which means it has the potential to grow nice crystals. You have round floret crystals on the rim, and they open up to spike and cluster formations down towards the pooled glaze. This is the second indication peak temp is slightly too high: you have lost enough zinc in run off to effect crystal growth. There is white to blue colorant in the crystal formation: this also indicates too much material ran off and pooled. However: notice the crystals have growth rings: although not as pronounced as you would like. Adjust your soak temperature ( not peak) down by 10F- it will make the crystals fill in: "florets." 

190826smGr1903B1.jpg

This sample shows peak temp is too high by the pooled run off with crystal growth on the rim only. For your notes: copper and nickel like about 10-20F less peak temp than cobalt, iron, and manganese.

190826smGr1903B1b.jpg

You have inner and outer growth rings: just need a mild downward adjustment in ramp hold (growth) cycle temps. Do not worry about the crazing at this point. Dial in your peak melt temp, then your growth cycle temps : then adjust silica to control crazing later.RULE 1: only change one parameter at a time when testing crystalline: so you know exactly which change caused what reaction. Final assessment: you did exceptionally well for your first time out with this glaze- be proud.

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Just now, JessHobbyPotter said:

dud 1: first time it was Shimbo's Tin Foil II base glaze with no colorants.  This time I added cobalt 008 on the rim and Turnidge MFE with no colorants... just the cobalt on the rim.

dud 2: first was Shimbo's Tin Foil II base glaze with CuCo3. This time I added Turnidge MFE with no colorants.

refired dud 2.jpg

Notice the streaks running down the side walls? In this case: that is the tin and zinc pooling to the bottom. Lose too much colorant- blotchy crystals. Lose too much zinc- no crystals. In dead center bottom there are too large blotches with raised rims. That is called "boiling" in the crystalline world. It is caused by excessive peak temp; but also common when excessive lithium carb is used in the recipe. Cobalt is reactive to excessive heat and/or excessive flux: boiling is a direct indication of those problems.

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Just now, JessHobbyPotter said:

Kiln 2 with a different schedule (unfortunately before I saw Glazenerd's advice about reducing the temp in the first schedule a bit).   First, here are the 2 duds from before.  I added more glaze and refired.  The third is my favorite glaze from last time on white clay instead of brown. Apparently this will be three separate replies.  Sigh.

refired dud1.jpg

In the crystalline world this is called: "Crap." If you do not get results in the initial firing: odds of recovery in a second fire is slim to none. However it is a good lesson of how colorants and oxides disperse in a firing. Notice the large run lines of the cobalt and the white streaks (tin) going down the sidewalls. This is also a good lesson on glaze application. Vertical pieces- 0.65-0.75 grams per square inch. Flat surfaces- 0.45-0.50 grams per square inch. When glaze application is excessive: it will pool and crystallize. A good record none the less: you now know what excessive glaze application looks like. To further explain technical terms: when you open the kiln expecting beautiful crystals and see this: the immediate reaction is "crap." Descriptive on both a chemistry and emotional level.

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2 minutes ago, glazenerd said:

By the way- stay far away from acid baths: dangerous if you do not know what you are doing and do not have the proper safety equipment. 

What's the danger? I mean other than the acid itself

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Liam: acid etching usually involves full strength muratic acid with only mild dilution. Typically the PH hovers around 1.5- very corrosive to skin, eyes, and inhalation of fumes can damage lung tissue. Not only requires eye and skin protection, but also respirator for those specific fumes. If left to soak indoors: can rust any metals within a few feet within hours. Seriously bad idea to make that suggestion to a screen name with "hobby" in it. Yes, I play with some potent stuff: but I have the safety equipment, and the training (EPA) to do so. And I dispose of it within recommended guidelines. 

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18 minutes ago, glazenerd said:

By the way- stay far away from acid baths: dangerous if you do not know what you are doing and do not have the proper safety equipment. 

So... I am a certified chemistry teacher, and I have access to a hood at the university where I now work.  BUT, I respect that I have a lot more to learn about the basics before I start with anything like that.  : )

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2 minutes ago, glazenerd said:

Liam: acid etching usually involves full strength muratic acid with only mild dilution. Typically the PH hovers around 1.5- very corrosive to skin, eyes, and inhalation of fumes can damage lung tissue. Not only requires eye and skin protection, but also respirator for those specific fumes. If left to soak indoors: can rust any metals within a few feet within hours. Seriously bad idea to make that suggestion to a screen name with "hobby" in it. Yes, I play with some potent stuff: but I have the safety equipment, and the training (EPA) to do so. And I dispose of it within recommended guidelines. 

I see, I have seen people use milder dilutions for longer periods, also other corrosive/reducing agents like dilute ammonia or sodium metabisulfate, which are still also dangerous.  

Isn't the folk tale about the discovery of the acid bath thing from soaking them in wine?  How about a week in vinegar?  I don't have EPA training but I've dabbled with some acids in my day.  Didn't think it was a big deal!

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8 hours ago, Hulk said:

Nice!

...there's some crazin'; how thickly applied?

So, I like the crazing, but I can show you how thick.  I have been taking pictures of every step.  Note that the glaze is not brushing well.  I will be increasing the amount of glycerine in the future to address this.

beforefire.jpg

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jess, are you wetting the pot a little while before applying the glaze?   dry bisque sucks all the moisture out of the brush before it makes a complete stroke.  quickly dunking the piece in water before you prepare the glaze, brushes, clean area is probably enough time to let it work.

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Ah, was curious! It's all melting in well.

I don't brush much glaze, but when touching up, or accenting chatter marks (especially), I'll pick up some water with the brush, then glaze - the water is drawn in by the thirsty bisque, and the glaze can glide on ….for a moment or so, before it starts to drag again. For chatter mark accents, I'm looking to fill the marks and minimize wiping away excess later on. I'm also brushing glaze onto the bottoms - within the foot - same approach, floating a thin-ish layer of glaze on water.

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