A Demonstration of How 18th Century Slip Decoration Appears on Broken Shards

This report was a special request from a very knowledgable reader. I have recently written about kaolin clay that was used for yellow slip decoration. When kaolin is applied, its white, but after the chemical reaction with lead glaze in the kiln - it turns yellow. The reader was interested in seeing any shards that may have partially lost some of the yellow slip in breakage. They wanted to see how the slip decoration appeared. I have taken sample shards from the Charlestown, Massachusetts archaeology collection and the Clough House archaeology collection in Boston's North End to demonstrate this idea. Both English and American products are seen to show that the technique is similar in both countries - and its really universal around the world.

(Yellow) Slip Decoration

Pre-1775 Archaeological Context

Probably Charlestown, Ma Made Redware

Charlestown, Ma Archaeology Collection

Photo Courtesy: Boston Archaeology Department - West Roxbury, Ma

Slip Decoration that Still Appears White

 Pre-1775 Archaeological Context

Probably Charlestown, Ma Made Redware

Charlestown, Ma Archaeology Collection

Photo Courtesy: Boston Archaeology Department - West Roxbury, Ma

(Yellow) Slip Decoration

 Pre-1775 Archaeological Context

Probably Charlestown, Ma Made Redware

Charlestown, Ma Archaeology Collection

Photo Courtesy: Boston Archaeology Department - West Roxbury, Ma 

(Yellow) Slip Decoration

 Pre-1775 Archaeological Context

Probably Charlestown, Ma Made Redware

Charlestown, Ma Archaeology Collection

Photo Courtesy: Boston Archaeology Department - West Roxbury, Ma 

(Yellow & White) Slip Decoration

Pre-1775 Archaeological Context

North Devon, English Redware

Clough House Archaeological Collection - Boston, Ma (North End)

Photo Courtesy: Boston Archaeology Department - West Roxbury, Ma 

(Yellow & White) Slip Decoration

Pre-1775 Archaeological Context

Probably Charlestown, Ma Made Redware

Charlestown, Ma Archaeology Collection

Photo Courtesy: Boston Archaeology Department - West Roxbury, Ma 

(Yellow & White) Slip Decoration

 Pre-1775 Archaeological Context

Probably Charlestown, Ma Made Redware

Charlestown, Ma Archaeology Collection

Photo Courtesy: Boston Archaeology Department - West Roxbury, Ma 

(Yellow) Slip Decoration

  Post-1775 Archaeological Context

American-Made Redware, Origin Unknown, Possibly Pennsylvania-Made

Charlestown, Ma Archaeology Collection

Photo Courtesy: Boston Archaeology Department - West Roxbury, Ma

Non-Slip Decorated Shards

All Glazed with Variations of Green

No Kaolin Used

  Post-1775 Archaeological Context

American-Made Redware, Possibly Massachusetts
Charlestown, Ma Archaeology Collection

Photo Courtesy: Boston Archaeology Department - West Roxbury, Ma

Sometimes kaolin was used under various colored glazes; however I am not sure why potters did this. It is interesting to see when the kaolin was originally applied it appeared white in color; but when the slip was exposed to the heat of the kiln and a lead glaze, a chemical reaction occurred that changed the color to yellow. From the shards, it is evident only the parts of the slip directly exposed to the kiln temperature and the lead glaze showed a change in color. The layer underneath apparently remained white in most instances. Examples of both English and American slip are shown and this chemical reaction appears to have happened in industries all over the globe. It's assumed this chemical reaction was not regional or continental either, but rather it happened in almost all industries. I cannot say for sure if it happened all the time because that would speak for every single example of slip known - rather, in most instances the above evidence is what typically happened when a potter applied slip and then fired their product in the kiln. It's rather interesting to see first hand!

Much More to Come...