Slip Glazes

[George Lewter]

Slip glazes are glazes developed from natural materials that might be usable as clays in a low fire range, but actually melt down and become complete or nearly complete glazes at mid or high-fire temperatures. Albany Slip, Alberta Slip, and Ravenscrag Slip are examples. You might have such a slip in a nearby stream or riverbank, though it might be more of a high fire clay.

[George Lewter]

Norm Stuart added the following to another discussion. I deemed it worthy to be included in a new topic of slip glazes - - - -

Our studio still has 2/3 of a 50 pound bag of Albany Slip which is not very popular.  Every time I use it in a glazes, it looks like a brown electrical insulator or a very dark nearly black tenmoku.  It's surprisingly difficult to find textbooks with original recipes for Albany Slip - I've needed to visit reference libraries. 

I've found people think a glaze colored with of Tin Oxide and actual Albany Slip is too dark and "doesn't look like Albany Slip" as this space in people's minds is now occupied by Amaco "Albany Slip" they buy in pints.  I'm sure I own a bag of a ceramic conservator's dream come true.

Actual Tin Oxide Albany Slip is a much darker brown with whites.  But this photo is how people prefer to remember it.

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Permalink Reply by Norm Stuart on February 19, 2014 at 3:25pm

 

Classic Albany Slip Glaze - what was all the fuss about?  It was inexpensive and easy to make.

85%  Albany Slip

13%  Lithium Carbonate

  2%  Bentonite  (with added Calcium Chloride)

I can create a duplicate of this "Insulator Brown" using frit, kaolin and Mason Stains.  As Albany Slip was mined, the chemical composition constantly changed with the ore body.

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Permalink Reply by George Lewter on February 19, 2014 at 5:53pm

 

I would say that the classic Albany Slip Glaze was exactly that Albany Slip, nothing more, which might explain the dearth of recipes. It was virtually defect free at cone 10 and a good fit for porcelain and stoneware. Very widely used for used for common jugs and crocks before it appeared on every power pole in America. It was chosen for reasons of economy, simplicity, durability, and its glossy, sanitary surface. It was also a time when earth tones reigned, and dark brown was perfectly acceptable. It was not a cone 6 glaze. 

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Permalink Reply by Norm Stuart on February 20, 2014 at 12:39am

 

My Grandparent's had similar period furniture, all dark mahogany or ebonized wood (black).  So it fit the ethos of the time.

The few original Albany Slip and Tin recipes I've found all work well at Cone 6 with the addition of 13% Lithium Carbonate, just as Albany Slip by itself.  But they're always a much darker brown than Amaco's Cone 6 re-imagined version.

Doing a search of original albany slip glazed ware, this has the lightest color of any, so likely Albany slip with tin.

http://prockscrocksantiquestoneware.com/red-wing-stoneware-albany-s...

Many Albany Slip glazes are so dark they're nearly black like the earthenware pig jug below.  Wesley Cowan, who auctioned this piece, says these glazes had additional Manganese Dioxide added to the glaze so are not food safe by today's standards.  For some reason appraisers sometimes call this Bristolware, although

http://www.cowanauctions.com/auctions/item.aspx?ItemId=60674

Commercial stoneware jugs with Albany Slip are probably the most widely recognized, usually with added manganese.

Norm Stuart added the following to another discussion. I deemed it worthy to be included in a new topic of slip glazes - - - -

Our studio still has 2/3 of a 50 pound bag of Albany Slip which is not very popular.  Every time I use it in a glazes, it looks like a brown electrical insulator or a very dark nearly black tenmoku.  It's surprisingly difficult to find textbooks with original recipes for Albany Slip - I've needed to visit reference libraries. 

I've found people think a glaze colored with of Tin Oxide and actual Albany Slip is too dark and "doesn't look like Albany Slip" as this space in people's minds is now occupied by Amaco "Albany Slip" they buy in pints.  I'm sure I own a bag of a ceramic conservator's dream come true.

Actual Tin Oxide Albany Slip is a much darker brown with whites.  But this photo is how people prefer to remember it.

[Norm Stuart]

 

[George Lewter]

 

[Norm Stuart]

 

[George Lewter]

Ravenscrag slip is a material that is a complete, stable glaze by itself at Cone 10, and requires some additional flux at cone 6. Plainsman Clays in Canada and Tony Hansen have done extensive testing and development with Ravenscrag slip that is well publicized on the Web. Though I purchased and did a few tests myself a couple of years ago, I was not particularly impressed with my results because the outcomes did not appear "unusual" to me compared to other glazes that were more exciting. Working at MIY Ceramics in Hollywood, FL, I found that one of their studio glazes they called Pavarotti Gold is actually the basic cone 6 mix of Ravenscrag slip 80g and Frit 3134 20g. To this base - add 6% red iron oxide and 2% bentonite. The resulting glaze is a rich amber that does beautiful things over widely used glazes like Nutmeg, Spearmint, Licorice. 

Pitcher lined with and rim dipped in Licorice. Exterior bottom 2/3 dipped in Spearmint. Exterior top 2/3 dipped in Pavarotti Gold (local name for the glaze) on Highwater Little Loafers white stoneware body. One hour hold at 1740 deg F on the cooling ramp.

Bowl layered with Spearmint over Nutmeg. Fired once and there was some blistering in the bottom. Reglazed the inside with Pavarotti Gold and refired.

Find the homepage for Ravenscrag slip at http://www.plainsmanclays.com/ravenscrag/index.php

Their cone 6 recipes are at http://www.plainsmanclays.com/ravenscrag/index.php?recipes6=1

Back in my studio, I will be looking much more closely at Ravenscrag slip based glazes and trying them layered with each other and with my stock glazes.

[Jeff Poulter]

Hi George,

     What were the deletes on this page?  Just curious.....  jhp

[George Lewter]

Jeff, no deletes were made. You were seeing artifacts of delete links from copying and moving a series of postings from their original location (where it was possible for me to delete comments, using my super powers as editor).