Clay Additives

[BlackandWhitedogpottery]

Hello everyone. 

 

I have a goal I would like to accomplish but I would like to run these ideas by first. 

 

My 1st goal is to have a smooth clay body with faint to light orange round speckles, my 2nd is to have long brown bleeds going down the side of the pot. 

 

I have been using speckled buff from my clay supplier but I would like to try my own. I have a white glaze I intend on using for this so I'm mainly working on additives to a smooth buff clay body I buy that I fire to cone 6

 

My Idea was adding percentages of iron oxide to the buff clay, ranging from 1%-5% to 15%-25%, mixing it with dry ground clay and then mixing as a slip then firing to cone 6. Taking this then grinding/sifting through fine mesh. Mixing in percentages to wet clay and going from there. Has anyone had any similar experiences? 

 

I would like to avoid Manganese since I'm a little leary about it, and I have thought about iron shillings but I was looking for something a bit more backed by "set in stone" recipes and additives to clay

 

Thank you

 

[Marcia Selsor]

"My Idea was adding percentages of iron oxide to the buff clay, ranging from 1%-5% to 15%-25%, mixing it with dry ground clay and then mixing as a slip then firing to cone 6."

First, taken to ^6 you could not grind this without a hammer mill. Try taking it to ^08 and small with a hammer.

 

Sounds like you are after a reduction look on your clay. You won't get that by adding iron and using an electric kiln.It is the reduction that brings the iron to the surface of the clay.

 

Also 15-25 %iron would make the clay brittle, unusable in a microwave, etc.

The most simple thing to use and what oxidation potters used for decades is granular ilmenite.

As for the runny streaks, you could dry up a dark graze, gently pulverize it without getting too fine. then try rolling a damp leather hard for over the glaze bits so the enter the surface of the clay. You really don't want runny streaks throughout the clay body and onto the kiln shelf or slumping your forms.

 

Marcia

[BlackandWhitedogpottery]

I've didnt know of the reduction technique, I thought that was a only for porcelain and copper reds. I was just thinking an iron "grog" would work similar like pieces of trash iron that show up in stoneware clays with white glazes

 

I will look into granular ilmenite. Would it make light light orange?

[glazenerd]

I use ilmenite often in crystalline glaze: some for color, but more often as a titanium source. Iron chromate does some interesting things in clay. Thinking- granular rutile would be a good option as well.

Nerd

[Marcia Selsor]

yes, granular rutile would yield a lighter color than the ilmenite. I wouldn't put iron chromate in clay because of the chrome. Toxic and chrome penetrates the skin.

Marcia

[Magnolia Mud Research]

I often use crushed bisque passing a 60 mesh screen as a surface grog.

I also use a terra cotta concrete stain as a colorant especially for making surface marks on pots.  

If you mixed the stain with water and soaked the crushed bisque in the water, and then dried the stained "grog" you should get a nice orange color in the specks and it would be based on the same clay body as the pot. 

 

Mix the home made grog in with some slip and slather away.  

 

[i have made grog by rolling 3 mm thin slabs, bisqued, crushed with a hammer and sieved.  Could also stain the slab before bisque and get any color you wanted.]

 

LT

[BlackandWhitedogpottery]

I did run a quick test of adding RIO to slip just out of curiosity at my last firing. It looked like minute specks of pepper that came up in the clear glaze and hardly showed in the tin glaze. 

 

So. I have granular rutile on order right now. Any recommendations on how much to add for light speckling?

 

I did add 2% of the soft bisque grog to wet clay last time and it was pretty speckled from what I could tell.

 

I have found percentages for glaze but not much for clay.

 

Lastly..I have searched but haven't found anything that flat out says it but are there any real issues with granular rutile? (toxicity..)

 

 Thank you

[Charles]

It looks like all the posts so far are about glazes, but I have a question about clay.

I'd like to create one or more clays with a lot of varied inclusions for visible texture.

I just started making my own grog using a "dolly pot" small portable rock crusher, breaking up bisqued thin slabs of several clays and sorting them by mesh range.

I decided I'm not interested in anything smaller than 40 mesh, as it just looks like dust to me.  I do realize that commercial grog can be close to 10 times smaller.

I gave my studio manager a list of my planned inclusions, and asked if he could come up with a recipe for the other 70%, preferably yielding a dark and rich brown.  I saw an example of the color I'd ideally like, but believe I shouldn't attach other people's photos - I haven't actually checked site policy on this.  Perhaps it's OK with accreditation.

1 %     Ilmenite

1%      small coal slag pellets ~1 mm

2%      granular feldspar  OR molochite - half each?

2%      6-10 mesh crushed granite

2%      medium sand

2%      large sand

10%    10-20 mesh homemade grog - ~ five mixed colors

10%    20-40 mesh homemade grog - ~ five mixed colors

------

30%

 

While he ponders this, I'm wondering about the possibility of adding this to wet clay?  I realize the distribution wouldn't be as even as it would with dry clay, no matter how long I work at it.  I want to try a test, and mostly wonder if anyone has done something similar, or am I crazy to even consider it?

 

 

 

[liambesaw]

That looks like a lot, I have wedged granular magnetite and illmenite into wet clay, but 30% would be a lot of wedging and adding water as well because half of those will suck water right out of the clay.  Might be rough.

[glazenerd]

Charles:

one of the parameters about clay: when the glaze surface reaches peak temperature, it can take an additional 30 minutes for the core of the body to equalize. Several lab controlled studies on this topic from years past. This is where the modern practice of doing holds at peak came from: that said-

Any type of granular material will not be fully incorporated into a melt unless extremely long peak holds are observed.

granular coal has carbons: sulfides to be precise: which will cause bloating.

granular feldspar will cause pinholes and blisters: granular calcium will produce lime popping.

the other materials should be okay, long as particle sizes do not get too large. China sand is a good option, clean as sand goes.

t

[JohnnyK]

You might check out Kathleen Standen's book here: https://ceramicartsnetwork.org/shop/additions-to-clay-bodies/

[Charles]

Thanks for the info glazenerd.

 

I thought granular feldspar fired to ^11 and higher produced the white rounded surface effect seen in Shigaraki ware - or is this what you mean by blisters?

 

Granular feldspar fired to ^10 will produce pop-outs - as seen in this photo of Grogzilla.

 

I became interested in coal slag after seeing Perry Haas' work.  I've tried the small pellets used for commercial surface blasting work, and they just create small black specks when they are at the surface.  I obtained some raw slag and broke it down to ~1/4" chunks - I just got a bisqued piece yesterday and immediately put it on the high-fire rack at school, unglazed as I wanted to see the surface result.

 

I don't know if any of what I listed contains granular calcium, or if you are just drawing a comparison to feldspar.

 

As far as firing sequence, I'm at the mercy of what the school uses, however from what you state as modern practice I'm sure they would do the hold.

 

OTOH - since I'm exclusively interested in surface texture, I'm not aware of any reason I should be concerned about what happens on the interior of the piece?

 

I may reduce the granite size to 6-10, but like them to look rocky.

 

[glazenerd]

Charles:

if you are firing for effect, with non-functional use: then the door is open for any option. Enjoy! If you run into specific problems, the list I provided will give you insight to which addition would be suspect.

Tom

[Charles]

Last spring I was breaking up granite chicken grit on a metal table with a large-head hammer.  I had the grit in a heavy weave fabric, but it was still a pain to gather the results, and repeated use wore it out.  This fall I discovered miner's dolly pots, designed to be taken into the field.  I started with the small, but moved up to large (13 #).  I do recommend using this on a hard surface, such as a concrete floor or a cinder block.  As a point of reference, they are designed for quartz (to look for gold), which is harder than granite.

https://www.blackcatmining.com/mining-equipment/crushers.cfm

If interested, you might want to order soon, as the owner Eathan (great customer service - ask for lower cost USPS vs. UPS shipping; the site only handles the latter, but he'll refund the difference) told me that the fellow who makes them is retiring - unknown if he will be able to find another source for them.   The big benefit for me is that everything stays in the tube, so I can easily feed it into my smallest screen, or an intermediate container. 

I use a 20, 10, 6 and then 4 mesh.  Anything that doesn't fit through that I just put back in the next cycle.  Since I want it for visual effect, I consider anything smaller than 20 mesh as powder, with no need to differentiate it further, and will sometimes dust it onto a clay surface to add hints of another color.

 

The main reason I'm replying now is something I just realized, based on a comment in an old Alfred Grinding Room Cookbook (I've been making some interesting - often groggy, clays based on recipes from 2004-2007) that relates to the initial post.  I had been rolling thin slabs, sending them through bisque, and then breaking them up and screening.  Before making the grog I had just been breaking up the dried slabs and using that directly.  I switched when I wanted to include foreign clays in new bodies I was making, vs. rolling them into slabs of commercial clay. 

Anyway, instead of having to break up fired clay, it makes much more sense to do the breaking and screening with the dried clay, and then sending that through bisque.   I saw this in reference to 10-20 grog, so if you're looking for something finer it's possible that the clay bits might tend to reattach in bisque?  Also, this fellow was coloring his clay body with 10% Mason stain before drying it out, if anyone is looking for colored grog.  

As mentioned, I had formerly been using broken up clay bits, and I'm still not sure that wouldn't work just as well as grog - for visual effect.   Here is an early "slab-wrap" cup from mid-winter with mixed clay bits rolled onto the slab before forming the cup.  My studio manager suggested that the clay bits would have the potential of absorbing some water from the moist clay.  However, the clay body has often peeled back some from the larger chunks, suggesting that any water the main body lost was not transferred to the dried clay.  Again, this may be different for small mesh sizes.  YMMV

 

BTW - I noticed that I spoke of raw coal slag in the previous post.  Here's the plate out of high-fire.  I love the rusty Death Valley clay, but wish I had varied the size of the coal slag more (or only used fewer and smaller pieces), as there are too many largish metallic-looking bumps for my taste.  I'll likely not use them for plates again - although, I've been using this for Cape Cod Dark Russet chips.