glazenerd

Goatrider:
In the first pic, very small cracking on the rim. That indicates you need some ball clay: start at 10% OM4 or equal. The green color is from calcium usually, other minerals will present that color. From the color of the second pic: 6-8% iron content. Final blob pic: lack of alumina is the biggest factor of pyroplasticity (melt). Kaolin is 37% alumina: whatever kaolin you have on hand. Wild clay 75%, ball clay (OM4) 10%, kaolin 15%. Will get you started, but will have to check melt before you dive any deeper.
Nerd

Looking closely, I can see pinholes that are clear. I can see others that are black. I will vote coffee.
Tom

I work with porcelains  at cone 10 ,Daves Porc (99.9%) and some Babu and some 50/50
for salt pots its mostly iron bearing stoneware with a small amount of Porcelain  again cone 10 from Laguna clays

I use two clay bodies, one for cone 6 soda firing and the other is a local clay that fires at cone 03.
The cone 6 body is Laguna B-mix 5. After trying various clays I found it responds well to soda as well as hot and cool spots in my kiln. It seems easy to throw for me and is pretty tolerant when my craftsmanship isn’t perfect. The downside is it’s expensive compared to other white stonewares.
The local clay is something I’ve played with for many years and gotten to know. It isn’t tolerant in any way! I add 1-1/2% Veegum to it, the biggest monetary expense. It cracks, slumps in hot spots, and is left porous in cool spots. I have to be completely on my game to make it work, which is part of its charm. I haven’t tried to calculate the cost, I’m afraid it would be too discouraging. 

Three; white, red, and buff with speckles stoneware.
The first two are mined, processed, and sold by a local (Sacramento) company; the speckled buff is a Laguna product that they carry.
I'd been working on fitting my liner glaze to white stoneware, then tried a different clay, voila! ...haven't changed the liner glaze formulation since, although I did switch clays.
I like each color - and the glaze response to each - too much to give any up just yet.
Each is the "best of" so far.
Prior white stoneware got me working on low COE liner glaze, were not as plastic, had higher rate of "off-gassing large particle defect" and cost more to get, being further away.
Prior red stoneware, not as plastic, narrower glaze firing range (much), higher rate of particle defect, poor drying behavior, cost more to get.
Prior buff stoneware, narrower glaze firing range, cost more to get.

I use Laguna's buff for throwing and  Laguna's  Speckled Buff, Red Standard ,  Red  Calico and Death Valley for hand building.   The handbuilding clay's I use fire to different colors,  I like to work with different colored clays in one piece.  I use to make my own clay before premixed clay was readily available and affordable,  life gets busy and you get older  something has to be sacrificed.   Denice
 

I mix my own clay.   Firing with wood is a very harsh environment therefore I need to have a clay body with certain qualities that i doubt i can get out of an off the shelf clay.  I've had to adjust the formula several times over the years as problems pop up most of which are in the mined materials changing causing various problems in the body. The last problem I faced was bloating caused by a grog and too much of one particular clay. Changed that and I'm back on track. .... till the next problem rears its ugly head.  I  dont know if being in control of the clay body is a blessing or a curse. I tend to lean towards the former.

I think the last time I bought commercial clay was 10 plus years ago? I have blended a lot of wild clay, but that is really outside this topic. I blend two porcelains primarily: the first is for tile work, the other for crystalline glaze. The tile body centers on laying flat without me having to flip, weight, and baby sit it in the process. The porcelain for crystalline centers around a chemistry that does not hinder or interfere with crystal growth. They both met basic formulation standards; cone 6, absorption hovers around 1/2%. Not a fan of sodium based body fluxes for many reasons. Side note: I use the same basic tile body for throwing with minor adjustments. I purposely blend it to be a touch on the short side to allow for water absorption. The only red clay I blend comes from hematite bearing wild clay; which keeps a deep red color at cone 6. 
Tom

Babs
Zinc is processed two ways: the French process and the American process. The American process is just simply “roasting” (we call it calcining) that removes impurities. It is denser because it typically 80% pure, with 20% of various minerals commonly associated with zinc. The French process involves vaporing zinc at higher temps, resulting in a purity above 99%. It is finer, with less density. The zinc you are looking for is called Maximo 910 in the States, unless it has been sold to another company yet again.
Tom

About all I fired was tiles. I a 6.5CF square top loader, and a 15.5CF front loader. The easiest method is to calculate your current tile size (in setters?), to come up with the width x length x height. You mentioned upright? ( see below). My top loader has 3” brick, with 1” insulation: extremely energy efficient. Front loaders are the easiest ergonomically, but have more hot and cold spots. When the temp gets into the 1800F plus range: static pressure likes to push the bottom of the door open ever so slightly, which allows cool air into the bottom front of the chamber. Easy to rectify with insulation. The upper rear of the chamber tends to fire hot, which I remedied by drilling a hole from the top; into the rear corner of the chamber. If you fire speciality glaze that is fickle to temperature variations; then a kiln vent would be advisable for a front loader. If the pic I posted resembles what you are doing: then it a simple matter of calculating how many setters wide, by how many setters deep, by how many setters tall: to arrive at a chamber size. Allow 2” of free space around the edges, and calculate space required for shelves and legs. 
Tom

Babs
Zinc is processed two ways: the French process and the American process. The American process is just simply “roasting” (we call it calcining) that removes impurities. It is denser because it typically 80% pure, with 20% of various minerals commonly associated with zinc. The French process involves vaporing zinc at higher temps, resulting in a purity above 99%. It is finer, with less density. The zinc you are looking for is called Maximo 910 in the States, unless it has been sold to another company yet again.
Tom

Morgan:
If the Frost is combined with other clays as part of your total reclaim: then no specific protocols are necessary. If you plan on using Frost specifically, then you do need to follow specific protocols. Yes, Frost reclaim would be more prone to cracking. Frost has 30-32% sodium based flux which in part plays a role in its rapid drying/cracking. Bentone MA is highly processed hectorite, with magnesium removed. To give you an idea of how fine BentoneMA is: OM4 runs 0.55 microns, Taylor 0.28 microns, and BentoneMA, below 0.15 microns. This means it does not take much water or throwing to wash it out. If you plan on reclaiming Frost long term, then it becomes an issue. 
Tom

RF
You want soft slabs for a particular forming process I assume? Yet, you also have to understand that “soft” clay equals higher water content, which adds to the warping issue. The more water in the clay; the more dried shrinkage, and increased risk of warping. As to your other listed issues:
1. Kaolin and fire clay have very low plasticity: but they have some. If you work centers around slab building/forming: then adding molochite 325 would be advisable. Molochite is a grog, and 325 is used when you are trying to maintain low absorption bodies. Unlike kaolin, molochite adds no plasticity, and actually will reduce plastic properties if used in high %. Start at 5% in small test batches. Molochite 325 is used often in slab/tile bodies to control warping. Do not fall into the trap of: if a little works good, then more will work better.” Adding too much will actually cause cracking when drying. 
2. 10% silica additions in stoneware/red body is the industry norm. If you use a glaze calculator: aim for a 5:1 SiAL ratio (5 parts silica to 1 part alumina)Like all things clay: too much silica can lead to cristobalite formation. Cristobalite will dunt your pieces during the cool down, usually around 400-450F range. 
3. Ball clay is the primary plasticizer in most all clay recipes. Slab/tile bodies need just enough to make it malleable, and too much adds to warping/shrinking issues. Secondly, not all ball clays are the same. 8% Taylor, 15% C&C, and 25% OM4: will all impart roughly the same level of plasticity. Ball clays absorb water, as their plasticity levels increase, and as their % in the recipe increases: likewise total water content increases.  
Tom

1st. understand that hand mixed clay, or even clay mixed in a Soldner will take a week to ten days before plasticity is achieved. 2nd Adding kaolin or Hawthorne will lower plasticity, not increase it: both of these have very low plastic values. The original recipe is 50% Redart, 15% Goldart, 15% Om4, and 10% silica. OM4 is a medium plasticity clay, and it is common to see recipes with 25% OM4 for that reason. C&C ball clay is about 40% more plastic than OM4; and is readily available and cheap. Use the original recipe, and simply change out OM4 for C&C. I dry mix all the ingredients before mixing. Both Redart and Goldart have higher sulfide content, which produces your brown clay at cone 5/6. The final issue would be “soft slabs”? Slabs for tile, or slabs for hand building? High plasticity in clay bodies intended for tile can come back and bite you in the form of warping when drying, and excessive shrinking.
Tom

1st. understand that hand mixed clay, or even clay mixed in a Soldner will take a week to ten days before plasticity is achieved. 2nd Adding kaolin or Hawthorne will lower plasticity, not increase it: both of these have very low plastic values. The original recipe is 50% Redart, 15% Goldart, 15% Om4, and 10% silica. OM4 is a medium plasticity clay, and it is common to see recipes with 25% OM4 for that reason. C&C ball clay is about 40% more plastic than OM4; and is readily available and cheap. Use the original recipe, and simply change out OM4 for C&C. I dry mix all the ingredients before mixing. Both Redart and Goldart have higher sulfide content, which produces your brown clay at cone 5/6. The final issue would be “soft slabs”? Slabs for tile, or slabs for hand building? High plasticity in clay bodies intended for tile can come back and bite you in the form of warping when drying, and excessive shrinking.
Tom

About all I fired was tiles. I a 6.5CF square top loader, and a 15.5CF front loader. The easiest method is to calculate your current tile size (in setters?), to come up with the width x length x height. You mentioned upright? ( see below). My top loader has 3” brick, with 1” insulation: extremely energy efficient. Front loaders are the easiest ergonomically, but have more hot and cold spots. When the temp gets into the 1800F plus range: static pressure likes to push the bottom of the door open ever so slightly, which allows cool air into the bottom front of the chamber. Easy to rectify with insulation. The upper rear of the chamber tends to fire hot, which I remedied by drilling a hole from the top; into the rear corner of the chamber. If you fire speciality glaze that is fickle to temperature variations; then a kiln vent would be advisable for a front loader. If the pic I posted resembles what you are doing: then it a simple matter of calculating how many setters wide, by how many setters deep, by how many setters tall: to arrive at a chamber size. Allow 2” of free space around the edges, and calculate space required for shelves and legs. 
Tom

About all I fired was tiles. I a 6.5CF square top loader, and a 15.5CF front loader. The easiest method is to calculate your current tile size (in setters?), to come up with the width x length x height. You mentioned upright? ( see below). My top loader has 3” brick, with 1” insulation: extremely energy efficient. Front loaders are the easiest ergonomically, but have more hot and cold spots. When the temp gets into the 1800F plus range: static pressure likes to push the bottom of the door open ever so slightly, which allows cool air into the bottom front of the chamber. Easy to rectify with insulation. The upper rear of the chamber tends to fire hot, which I remedied by drilling a hole from the top; into the rear corner of the chamber. If you fire speciality glaze that is fickle to temperature variations; then a kiln vent would be advisable for a front loader. If the pic I posted resembles what you are doing: then it a simple matter of calculating how many setters wide, by how many setters deep, by how many setters tall: to arrive at a chamber size. Allow 2” of free space around the edges, and calculate space required for shelves and legs. 
Tom

About all I fired was tiles. I a 6.5CF square top loader, and a 15.5CF front loader. The easiest method is to calculate your current tile size (in setters?), to come up with the width x length x height. You mentioned upright? ( see below). My top loader has 3” brick, with 1” insulation: extremely energy efficient. Front loaders are the easiest ergonomically, but have more hot and cold spots. When the temp gets into the 1800F plus range: static pressure likes to push the bottom of the door open ever so slightly, which allows cool air into the bottom front of the chamber. Easy to rectify with insulation. The upper rear of the chamber tends to fire hot, which I remedied by drilling a hole from the top; into the rear corner of the chamber. If you fire speciality glaze that is fickle to temperature variations; then a kiln vent would be advisable for a front loader. If the pic I posted resembles what you are doing: then it a simple matter of calculating how many setters wide, by how many setters deep, by how many setters tall: to arrive at a chamber size. Allow 2” of free space around the edges, and calculate space required for shelves and legs. 
Tom

Was going through old files, when I came across the papers Marcia Selsor wrote on crystalline glaze back in the 1970’s. I know she does obvara and raku now: so that bought up a question. 
Q: Did your passion about a certain form, glaze, or technique change, and what caused that change?
 
Tom

Was going through old files, when I came across the papers Marcia Selsor wrote on crystalline glaze back in the 1970’s. I know she does obvara and raku now: so that bought up a question. 
Q: Did your passion about a certain form, glaze, or technique change, and what caused that change?
 
Tom

Was going through old files, when I came across the papers Marcia Selsor wrote on crystalline glaze back in the 1970’s. I know she does obvara and raku now: so that bought up a question. 
Q: Did your passion about a certain form, glaze, or technique change, and what caused that change?
 
Tom

Sorry for the long step away: had eye surgery and just got released. C&C ball clay is 35-40% more plastic than OM4. So if the recipe calls for 25% OM4, then 15% C&C will have close to the same plasticity levels. You can just substitute the remaining 10% with clay. 
 
Tom

Besides the obvious issue with firing large slabs flat (dunting), the other issue is uneven heat. The side exposed to ambient kiln temperature can vary to the temperature under the slab in direct contact with the shelf; further adding to the warp issue. I have fire porcelain slabs up to 30” square by bisq firing them on edge. Use tile setters as shown, or prop them up using other wares. 
Tom

Talc has high magnesium, up to 20%: which can alter color. Ball clays need to be under 2.00% total iron and magnesium to keep the color on the white side. C&C ball clay would be a choice. Aluminum content dictates refractory limits. 
Tom

Talc has high magnesium, up to 20%: which can alter color. Ball clays need to be under 2.00% total iron and magnesium to keep the color on the white side. C&C ball clay would be a choice. Aluminum content dictates refractory limits. 
Tom