Wild clay is a slip glaze

[RobS]

Greetings,

I have a very interesting material on my hands.  Quick background.  My uncle has lived in this area for most of his 70+ years and is familiar with the local waterways and he had been telling me about a layer of clay in the Chemung riverbank for a long time.   Last summer we took a canoe and a couple of 5 gallon buckets and set out to find the clay.  Downstream a bit, we found the clay.  Two adjacent layers, a yellowish/brown and a gray.  Upon shoveling them into the buckets, my first thoughts were this stuff is too sandy for anything.  The gray was more wet and did feel a tad thixotropic which was interesting.  Fast forward to December when I thought I'd at least slake down some of the clay, dry it out and do some testing.

Slaked and turned into a slurry it stays suspended.  Upon sieving, it is 100% finer than a paper coffee filter (15 microns I'm guessing).  It passed through a reusable gold coffee filter (20 micron ?) as a thick slurry as it were plain water.  I had to add a little extra water to get it to go through the paper filter but it dripped through after a while.  There's no extraneous matter in this stuff.  I dipped a test tile in the slurry.  The slurry dewaters as it were sand.  Placed on plaster the wet slurry is able to be removed and worked within minutes.  Almost no plasticity.   I made test bars and a drying test disc.

I did not measure the wet to dry shrinkage of the test bars, but wet to cone 04 shrinkage is 1%.  At cone 04 the clay is super light and porous and probably absorbs twice its weight in water.  I didn't quantify it.  I put the test tiles in a cone 6 oxidation glaze firing and added a test bar and as an afterthought, a waster slab.  I was surprised when I opened the kiln and saw the tiles.  The yellow/brown clay is the one that fires a touch more chestnut reddish color.  This was a hot cone 6 firing with cone 7 ending at about 10 o'clock.  The melted lump in front of the test tile was a test bar marked at 30 mm for reference.  The test tiles are Standard 630.

This weekend, I'm going to mix the slurries with various ingredients and colorants to see what results I can get.  I have been looking at old Albany slip recipes to get an idea of what to try and so far I've come up with various concentrations of iron, frits, whiting, spodumene, gerstley, and some colorants.  I'll post pictures of tests later this weekend.  I'm super excited at the prospect of something interesting coming out of this. 

For the geology/hydrology folks out there, after a bit of research, I believe this material is old lake bed that survived the Wisconsin age in the river valley.  Quoted from USGS Professional Paper 379, this sure sounds like what I found.  First a general description of the area then a section where they explain each layer:

In the valley of the Chemung River from Elmira to
Sayre, lake beds underlie the glaciofluvial deposits.
The lake sediments accumulated in the narrow bedrock
valley of the river and its principal tributaries, and they
are older than the Valley Heads moraine of Fairchild,
perhaps antedating the Olean substage (MacClintock
and Apfel, 1944).

Lake beds; silt, clayey, calcareous, light olive-
brown {2.57 5/4), massive. Lower contact
sharp, wavy; local relief ranges from 2 to 3
inches. About 200 ft to the south this unit
changes to calcareous medium to fine sand,
about 2 ft thick that rests disconformably on
the lake beds of unit 4_ _____________________ %
4. Lake beds; clay, silty, calcareous, gray (57 5/1),
stratified; form varves ranging from 2 to 4
inches in thickness and consisting of a relatively
thick layer of silty clay that grades upward into
a thin layer of clay; the contact between two
varves is sharper than that within a varve___

 

Edited February 18, 2023 by RobS

[glazenerd]

Rob:

You have magnetite (iron) bearing clay; somewhere in the 7-9% total iron content range. Classic terra cotta at cone 04, and chocolate brown at 6+. You will get red in thin layers, but if you get it too thick- orange/tan to brown as it gets thicker. Must be slow moving waters for that distribution of very fine particles; bit unusual. Also surprised there is no plasticity; Ord humus (organics) commonly found in lake/river/stream collection areas. NY State also has an unique variety of smecites; which is also highly plastic. From everything I have seen and read; 1-2 micron particle sizes 

The note of interest to me: “stays suspended” and “no plasticity.” Those two do not fit clay chemistry with one exception: high calcium content. Calcium will keep fine particles suspended when “common plasticizers” are absent. The melted blob at cone 6+ indicates total alumina content is 15% or less. If you want to work with it, I will post some fixes. If not, enjoy the wild clay adventure.

Tom

Edited February 18, 2023 by glazenerd
I really dislike auto-correct.

[RobS]

Tom,

I appreciate the insights into my material.  I would like to at least do my due diligence with respect to the uses of this slip.  I would like to continue testing and working with this material in the vein of maybe finding an interesting glaze result.  I've seen Albany slip used to make some beautiful glazes like a nice black and a few different oil spot type glazes.  I know most of that work was done at cone 10+ and mostly reduction, but if I could come up with a glaze or two using this slip as the main ingredient at cone 6, that would be nice.  I think as a body, this material would need too much tweaking but as a glaze ingredient I most definitely would love any and all advice on fixing it or glaze addition ideas.

I have about 30 tests in the kiln right now and will post  pictures of the results tomorrow. 

Rob

 

[RobS]

Here's the results of my various tests with this slip clay I found.  I tested:

Test tiles are Standard 630 fired hot cone 6 oxidation.

various levels of RIO from 2% to 20%

frits 3124 and 3195 from 5-20%

spodumene, whiting, gerstley, rutile 10-20%

copper carb, cobalt oxide and carb, chrome oxide, yellow ochre

Most of the tiles were either chocolate brown or mahogany brown, depending on which base slip I used.  There were a few that are interesting.  The ones with whiting turned out a silky butterscotch color, the one with whiting and cobalt(242 in the pic) breaks glossy black on the edges and is an interesting shade of grayish/tan/brown where thick and the one with speckles is gerstley borate at 10%.  Also, there are a couple that are quite close and could be a very nice gloss black if I tweaked the cobalt/iron levels a bit I think.

I haven't done any durability testing as of yet.  I think I may try some triaxial blends or currie grids with whiting, cobalt, gerstley to see if there are more interesting things.

 

Edited February 26, 2023 by RobS
Add clay body and firing info

[RobS]

One more pic of the GB tile as I ran over my 1MB limit.

[Min]

Nice work! Thanks for sharing. Looks like you have some good possibilities there.