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Member Since 18 Dec 2015
Offline Last Active Today, 12:55 PM

#124534 Looking To Start Mixing My Own Glazes

Posted by glazenerd on Today, 12:52 PM

Seeing as though I am home early, weather shut us down yet again.


Frit choices are made by application: high gloss, satin, matte, some for lower fire use, some higher, some boron based, others higher alumina. Application determines frit choice: to start out: 3110 and 3124 will get you going across a broad range.

EPK is the common kaolin used, OM4 ball clay is also popular; I prefer New Zealand Kaolin.


Chemicals:   Mahavir or Custer for potassium feldspar; KonaF3 (minspar) for blended, and Nep Sy for sodium feldspar. Custer is iffy.

                     325m silica for all glazes, 200 m silica if you are doing high fire in specific applications. (or clay bodies).

                     Dolomite for calcium and magnesium, and talc for magnesium

                     Lithium carb for straight lithium additions, or spodumene and petalite for lithium feldspar.

                     Gerstley borate ( or equal ) for boron based glazes/ lower melt temps 

                     Alumina Hydrate ( needed in rare instances).... 1/4lb is plenty.

                     Bentonite... glaze viscosity.... 1/4lb is plenty to start.

                     Whiting... calcium source.

                     Copper carb.  cobalt carb, red iron ox... will give you plenty of color to start... with some choice stains.


This short list will get you well down the road and give you a working glaze base.



#124407 Qotw: Pottery Attributes In The Studio

Posted by glazenerd on 28 March 2017 - 05:22 PM

"other" for me, which I cannot explain without a bunch of techno-blather. Suffice to say I have spent seven year studying every aspect of crystalline glaze and the clay body it goes on. Two + years ago it occurred to me that the porcelain was causing just as much problems as the glaze. This summer I will actually put all that study to use and make things. Unless my calculations are wrong (they are not ) I should see some dramatic results.




side note: of course my throwing skills will have to greatly increase as well.

#124344 Sio-2 Clay - Porcelain(Black) - Black Ice

Posted by glazenerd on 27 March 2017 - 06:48 AM


I have to say, it is super soft. So soft that I almost want to wedge out balls and let them sit for an hour or so before I use it. I have never seen any clay this soft out of the bag

Then there has to be more than the 20% water content than stated in the specs.  Sounds like you are well above 25%.  The only other explanation would be a boat-load of plasticizers.



#124218 Qotw: Do You Have A Question For Us?

Posted by glazenerd on 23 March 2017 - 05:50 PM


Nerd: just wait and see what Pres has up his sleeve. I am very glad you helped me so many times! Hugs to you

Evelyne: it is my privilege and honor to call you friend...



#124183 Looking For A Bisque Schedule

Posted by glazenerd on 22 March 2017 - 07:46 PM

The greyer the clay; the more carbons in the clay body.

The browner the clay: the more carbons, iron, and feldspars.


I think you will find that in this case your bisque schedule will do little to cure pin holing.

In your glaze firing; use your schedule up to 2050F, and then drop to 125-130F up to cone 5.5 with a 15 minute hold. Your dark brown clay is full of iron and potassium: it is the potassium burping gas. Naturally occurring dark brown ball clay tends to have larger particles of feldspar minerals in them: which takes a little more heat to gas off.



#124126 Qotw: Do You Have A Question For Us?

Posted by glazenerd on 21 March 2017 - 09:58 PM

I say we changed this game up: Pres will post an answer, and we have to guess what the question is.



#124125 Sio-2 Clay - Porcelain(Black) - Black Ice

Posted by glazenerd on 21 March 2017 - 09:52 PM


Water content: 20%                                             Porcelain typically runs in the 22-24% range: so this is low comparatively.
Plasticity (IP Atterberg): 11                                   11 on the Atterberg Plasticity index) is considerd low plasticity.  (30 is high plasticity)
Carbonate content (CaCO3): 0%                           common for porcelain bodies.. no big deal.
Drying shrinkage: 5.4%
Firing shrinkage at Cone 6: 10.3%
Porosity (water absorption) at Cone 6: 0.0%
Dry bending strength: 3.1 N/mm2 bending strength at Cone 6: 39.8 N/mm2
Thermal coefficient (a25-500ºC): 54.3x10-7ºC-1


Assuming they listed drying and firing shrinkage separately: the total shrinkage would be 15.7% The typical average for porcelain generally runs in the 13.5% range. Taking this shrinkage rate, adding in the water content: and finally the 0.0% absorption rate gives me some indication of formulation.


Kaolin only holds water on the face of the platelet: it does not absorb water. So they add more water to increase plasticity: the reason you see higher water content ratings. Secondly, bentonite is the most commonly used plasticizer: it can hold 3 times it's weight in water: further adding plasticity. The higher water content, coupled with bentonite additions is what produces the higher shrinkage rate of porcelain.


In this case you have lower water content and higher shrinkage: why?  In this case, either a sub micron ball clay, or hectorite, or polymer plasticizer was used: or a combination thereof. I am going to go with sub-micron ball clay for two reasons: the first is the lower water content. Hectorite and polymer plasticizers can hold up to four times it weight: even more than bentonite. If either of these two  were used, the water content would be higher. Sub micron ball is more in line with the water content: but is also the reason for the 0.0% absorption. At cone 6, sub micron particles would need to be in the 15-18% range to completely seal the body: coupled with finer mesh silica and higher feldspar.


The COE value of 54.3x10-7ºC-1 is shown in it's mathematical formula: you just need to X out 54.3x10-7ºC-1, to know its 5.43. Typical porcelain runs 5.75 to 6.00 with bentonite and higher feldspar content: which also indicates to me ball clay was used because of this lower value.


Dry bending strength: 3.1 N/mm2;              is what we call green strength. This number is on the low side.

Fired bending strength at Cone 6: 39.8 N/mm2:             is what we refer to as MOR  (modulus of rupture.)  decent number.


The black color is from one of 2 things ( my assumptions).  it is from magnetite: a naturally occurring iron mineral which is black in color.  if memory serves, Italy has a lot of black sand on its beaches: and it could have been milled down for use in ceramics. I think black sand is lodestone, which is also iron bearing.


My thoughts on the matter anyway.


#124048 Colemanite

Posted by glazenerd on 19 March 2017 - 08:28 PM

I have been using Calcium Borate for a little over a year or so. Primarily produced from Turkish colemanite: 50% boron and 30% calcium (+/-): roughly twice the bang of gerstley borate. I started a thread about it back in Dec. 2015, and I seem to recall some posts about boron/calcium frits being mentioned. I have had no problems with it for cone 6 use: and I have used it (need to check this) up to 27% of batch weight. A borosilicate glaze with the right level of alumina can be highly abrasion resistant. I use I for a couple of floor tiles I make; I found it to be more durable, and a high satin sheen.





http://community.cer...calcium +borate

#123877 Diy Wheelchair Accessible Pottery Wheel

Posted by glazenerd on 16 March 2017 - 06:32 PM

Will let others respond, but posting to commend you on being inclusive.



#123821 Advice Needed! Cone 06 Clay With Cone 6 Glaze - Yikes!

Posted by glazenerd on 15 March 2017 - 10:39 PM

The fluxes in a cone 06 glaze are first: usually different than those used in a cone 6. Secondly, a cone 6 glaze can have as much as 50% less flux levels compared to cone 06. So you could fire these pieces ten more times, and the result will be pretty much the same. There is just not enough flux, or the right kind of flux for low fire glazes.


I could fill many paragraphs with the mistakes I have made, the misfires, and the "dumb" mistakes I have made. The good news, dumb mistakes are easily fixed by learning. I will say it for the 100th time: you learn just as much by the mistakes as you do by doing it right....such is the learning curve of pottery.



#123810 Qotw: What Shape Do You Prefer?

Posted by glazenerd on 15 March 2017 - 06:56 PM

Flat- as in tile flat. Nothing in particular catches the eye, or is visually captivating other than the glaze that is on them. However, $100 bills are flat as well: and flat tiles produce flat bills: so it works (for now).



#123711 Two Piece Molds

Posted by glazenerd on 13 March 2017 - 09:34 PM



Cute little toad it was.

#123669 Two Piece Molds

Posted by glazenerd on 13 March 2017 - 08:47 AM

TY Mdo..


That certainly put me in the right direction. Others came up, that showed much larger molds - 30-60".. which is more in line with where I want to go. I knew reinforcing mesh would be needed; but was not exactly sure about the placement.  Did a forum search, those likewise were for the usual pottery mold system/s.  Again TY.



#123613 Making Oven Safe Work..

Posted by glazenerd on 12 March 2017 - 08:04 AM

The long and short answer to oven ware is "flame ware" clay bodies. The primary focus is COE (coefficient of expansion). Expansion and contraction of the clay primarily, and finding a glaze that does so equally with the clay. The lower the COE, the less the clay expands and contracts. So do your research over using " flame ware pottery". I seem to recall this topic in a few threads, so use the search bar above to find them.

To get you started:



Tony has a good starting outline.



#123442 What's Your Favorite Clay To Work With?

Posted by glazenerd on 08 March 2017 - 07:06 PM

Nerd's Coma Porcelain (and variations thereof)


12 X 16 arch2