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An experiment in Fritware Zero3

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4 hours ago, High Bridge Pottery said:

Tried mixing up another slip with half of the Kentucky clay but it just turned into a solid mass when I tried to deflocculate it :huh: Think I must have added too much but I thought it would settle out not turn into a solid mass.

If you over-deflocculate it goes the other way. Kinda like chocolate seizing. Been there many times...

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Turns out I was trying to mix to a sg of 2.1 doing 100g water to 300g dry and needed more like 140-150g water for 300g dry ingredients. Starting off with 0.2% weight of the dry ingredients in Sodium Silicate and then adding a little more. Need to try out some Sodium Carbonate solution too and see if that helps.


Ran some tests with the Kaolin I have and they are all pretty porous using similar amounts to the ball clay. Also tried swapping Nepheline Syenite for Soda Feldspar. 

Did a few tests on B0118 and it went from 0.08 - 0.44% absorption. For some reason the thin slip test tiles had higher absorption than the little slip cast glaze tower but all under 0.5%.



Mixed up 4 different glaze tests to try and poured some onto plaster. Not really glazed, more a 1g lump of glaze melted so they are all pretty thick. Opened the kiln at 200c because I figured that should be similar to a boiling/freezing test with little effort. No bisque firing so once the glaze had dried I placed onto bone dry slip.












The high has crazed a lot, the medium has a cracks on each side and the other two don't have any crazing. The clay already had the cracks from drying as I am just pouring slip onto plaster.

Lots of different bubbles :lol::wub:


Total shrinkage is 10%, test bars went from 100mm wet to 94mm dry and 90mm fired. Here's the unglazed fired clay.



Edited by High Bridge Pottery
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  • 1 month later...

Finally got around to trying a bisque firing :D thought I would try 800c (1472f) first and go hotter if needed but seems to have gone pretty well. They sound like bisque, have to wait and see how they go in glaze application. Haven't got any cones that low so not sure what cone I managed.



I always used to do 100c/h for a bisque but this time I was up around 230-250c/h with no problems, a little hold at 100c just incase. Total firing time is 4 hours. Seems like I didn't have to be so cautious previously.


Here's the graph of the firing.


Edited by High Bridge Pottery
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Thanks for the update! Are you going to do some more tests at different temps to see how hot you can go with the bisque? I feel like the hotter the better to ensure good burnout? What's the melting point of your frit? 

I love how they did the transition element groove on your kiln. It makes so much more sense than the hard angle the US kiln manufacturers like to do.

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I wasn't planning on testing a hotter bisque unless I get some issues further down the line. 


There''s no exact data on the melting point I can find online other than it has a firing range 860-1060C. (1580-1940f)

Not sure if that means 860 is the melting point as I assume they are specifying when it's a usable glaze. I will add some pure frit to the next bisque to see if they are melting or not. 


Are they doing a hard angle with the coils still intact or more like a front loader with what we call hairpins where the element is unwound in the middle? I had a job winding kiln elements for a while, mostly for skutt kilns and they had a similar diagonal across the brick. 

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6 hours ago, High Bridge Pottery said:

Are they doing a hard angle with the coils still intact or more like a front loader with what we call hairpins where the element is unwound in the middle? I had a job winding kiln elements for a while, mostly for skutt kilns and they had a similar diagonal across the brick. 

Still intact, but a much harder angle that requires a couple pins to keep it from coming out of the channel at the bottom turn.


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Ran a few glaze tests with the low and lowest expansion glazes from a few posts above, I also tried dropping the clay by 10% and increasing frit and petalite but they settled out within 30 min and didn't leave a nice layer on the bisque so that wasn't a good idea.

Can't see much visual difference in the surface between the low and lowest expansion glazes, need to crack out the microscope and have a closer look but I feel the low expansion is better as I don't need the talc or zinc.


I was also interested in how quickly my kiln dropped in temperature from 1100c. The first 100c dropped in 12 min, the second 100c dropped in 15 min and the third 100c dropped in 20 min. Pretty quick but it's a small kiln with a not so great lid. 


Low: left has two dips of one second and right two dips of three seconds. Same for all the photos.






Also tried a few glaze/body stains at 3% and 7%, in the low expansion glaze. They advise sieving the glaze after adding colour but I neglected to do that to see how bad it would be. I have an orange stain too but ran out of space to attach more photos on this post and it was my least favourite.



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I am very happy with the results so far :D especially after being educated in cone 6-10 and thinking that's the only way to get functional/vitreous ware for a long time.


Glaze needs some more testing to make sure it's durable and resistant enough but I can't see any problems with the low bisque. Having a quick look at the cone04 limits I seem at the higher end of Silica and Alumina and hopefully a good sign.

They are all a bit thinner than I would make functional ware so the extra thickness could cause issues burning things out. It seems mostly related to Lignite so maybe there just isn't much in this Dorset ball clay to cause problems.


It would be great to develop it into a throwing body too. Adding bentonite could mess with the porosity so more testing needed for that. 

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Had a look through my microscope at the glazes. The low expansion has smaller and fewer bubbles.

I did read on digital fire about holding on the way up and on the way down to reduce micro bubbles so I may try that next time and see if it actually reduces the bubbles. My guess is it wont from past experience but always worth trying.


Interesting that the purpleish stain seems to reduce the bubbles even more (or maybe the stain hides them) and the blueish stain makes the surface look a bit devitrified and must be more refractory. Going to do some experiments colouring slip instead so I shouldn't have much variation in the finished glaze surface and need a different glaze recipe for different colours.













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Having some strange results with my slip today. The first batch sat around for over a month and nothing crystalised out. I had a little left over and recycled all my dry slip into that a few days ago.

Added enough water but no extra  sodium silicate as the viscosity/sg were all good. The first casts were fine with no lumps but today I noticed these weird spots after I casting and on pouring out the slip I have tiny lumps everywhere. A little confusing when there was no issues with the fresh batch. It was sieved after recycling the dry slip and no issue using the next day but a few days later I have this problem.

Any ideas? I don't think it's any colder in the studio now than Dec/Jan, could being warmer get stuff to crystalise out?



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Good idea to sieve and see what they look like,  dunno why I didn't think to do that in the first place :lol: seems obvious now you say it. There's only a tiny bit of boron in the frit, much more alkaline frit.

First off it went though a 60 mesh sieve and.... hardly anything left on the sieve. Very odd.



Now I thought they looked way bigger than 60 mesh but just to be sure I put it through 100 mesh and ended up with a sandy looking substance.



Hard to tell any shape so I got a few snaps with my microscope, there's the odd black coloured piece but most are clear and white. Looks to be some long crystals and then lots of blob shaped ones. I will let them dry out over night and see if they dissolve tomorrow.




Edited by High Bridge Pottery
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I tried dissolving the crystals in hot water and they didn't dissolve at all. Could it be some kind of Calcium Silicate maybe?  Tried to search for a test to confirm that but nothing really simple seems to come up on google.


Maybe I could try a flame test if I can source some hydrochloric acid. I don't have any platinum wire but I do have nichrome wire. Probably a waste of time as I am pretty sure it's calcium related and the nichrome wire gives an orange colour too.

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Oolites then? But why would they be forming? Given the fibrous like structure of wollastonite is that acting like a seeding agent? Wonder what would happen if you used calcium carb to supply the calcium and adjusted the silica to balance if it would still happen? Is increased agitation contributing? hmmm, curious. 

edit: another thought, slip with dry scrap vs slip without scrap added, is there a difference?


Edited by Min
added a thought
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When I mixed up the slip from raw materials it sat around for a month or maybe even two without these little crystals appearing. It wasn't until I was running low that I recycled all my dry slip back into the left overs that I got these a few days after mixing.


I don't even really need the wollastonite, there just seemed to be a slight decrease in porosity adding a little to the recipe. The one I have been using is B0118 but I could take it out and only use Nepheline Syenite. I don't actually have a test with no Wollastonite but looking at the porosity it should still be below 0.5%.


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Interesting tests. (I didn't see this at first, thank you Min!)

What does jump out at me is the comment, "It's not any colder than..." By this can I presume that your studio is on the chilly side? (My historic low was 55 degrees at a studio, in a very poor part of town, many years ago.)

While I've never really thought "room temperature" had any bearing I do wonder what your actual temp is?

Also the state of the molds. Are they cold as well? Could the state of the molds, and the slip, be contributing to this problem?

My only other suggestion would be to take individual components and mix up small batches and leave them for a few days in the studio. Then, in an oversaturated liquid state, pour them out onto a plaster surface and see if any offer a similar reaction. You might get lucky and the offending party is obvious or maybe not?


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