Lab Summary Week 3: Pottery

Introduction

Our second lab was a venture into making pottery inspired by Early Medieval English techniques. After the fall of the Roman empire, many communities in England turned away from mass production and wheel usage in their creation of pottery. As we learned in our readings for the week, there was no longer a need on an economic or practical scale for lots of pots or ceramic wares; most were simply made domestically, on an as-needed basis. This combined with the higher manpower needed to operate a wheel effectively led to its decline in smaller communities once the Roman Empire pulled out of Britain. The pots of the Early Medieval English tradition are hand-built, often with embossed or etched/printed decorations in circular patterns. While none of us are experienced hand-builders, we got help from a professional; Carleton’s own Kelly Connole gave us a demonstration in pinch pot making and coil building, also teaching us about local Dakota ceramics practices. Then, we were turned loose to work on our pots and clay. 

Tempering

In our readings, we learned how delicate clay can be, especially when using primitive firing techniques. Mixing natural materials into clay can act as a natural protectant during the firing process, called a temper, to improve its plasticity and protect it from cracking, and reduce shrinkage (however, since we were using ‘industrial clay’ the added temper generally reduced the plasticity of the material). Because we are approaching our archaeological study of ceramics from an experimental angle, the goal of this lab was (aside from making some pretty cool pots) to determine what ratio of organic material would, when mixed into clay, most effectively combat shrinkage. 

To adhere to historical accuracy, we selected tempering materials which would have been familiar to early medieval potters: sand, gravel, and chaff (a sort of chopped organic vegetal material, in our case hay). Groups A-D and group F all used the same amounts of clay and sand, but changed the ratios of gravel and chaff which they used. Group A used a gravel to chaff ratio of 19:1, Group B used a ratio of 18:2, Group C used a ratio of 17:3, Group D used a ratio of 16:4, and Group F used a ratio of 15:5. Group E did not use any tempering materials, but used clay from the Arb, directly mirroring the early medieval English technique of using locally sourced clay. 

Day 1

After our demo by Professor Cannole, we jumped into mixing our temper with the clay, or mixing the crushed clay with water for group E. Then it was the long and tedious process of forming a pinch pot and adding coils to it. There was a lot of restarting and reworking the clay to get the right plasticity and workability, but students were successful in making at least one pot. Quite a few people went back for more clay for bigger pots, or for more pots, given enough time. Finally we measured them and put them on trays overnight. 

Day 2

On Friday we returned to our pots after a night of drying out. After reweighing and measuring our pots, we started to burnish and carve patterns into the clay. Burnishing is compressing the grains or fibers of the clay from a rough state into a more uniform pattern. This makes the vessel more water-tight and smoother. After burnishing, our pots had a gray-earth shiny color and a smoother texture. 

Various students chose to carve patterns into their pots as well, giving them some character. However, the gravel used as a temper proved to be hard to work around in both burnishing and carving, as both methods brought the inclusions in the temper to the surface of the pots.

Data

Until our pots are fired, we won’t be able to speak to how materials used affects overall pot-making success. However, each of us collected data on our respective pots measurements, right after making it and after one day of driving, and recorded the associated loss.

For Group A, which used the least chaff, pots seemed to retain about 90% of weight, and lose very little in terms of size. For example, here is Albert’s post-lab data.

	Original	After 1 day	Loss
Weight	553g	505g	48g
Height	11cm	10.5cm	0.5cm
Diameter (rim)	5.5cm	5.5cm	0cm
Diameter (widest)	8.5cm	8.5cm	0cm
Wall section	1.19cm	1.19cm	0cm

Group B, using the second least chaff, experienced similar results, though perhaps did experiences slightly more shrinkage. Because of our small sample sizes, though, it’s hard to make such definitive claims. Here is Siddharth’s data, which demonstrates an 88% retainment of mass after 1 day. The size in this group, too, did not decrease much, but seemed to be more constant across the different categories.

	Original	After 1 Day	Loss
Weight	574 g	507 g	67 g
Height	4.5 cm	4.4 cm	0.1 cm
Diameter (rim)	2.75 cm	2.6 cm	0.15 cm
Diameter (widest)	9.6 cm	9.5 cm	0.1 cm
Wall section	0.674 cm	0.525 cm	0.149 cm

Group C had perhaps the most variability across their pots, likely due to using a scale that was tilted slightly downwards for their original measurements. Because of this, many group members actually experienced weight gain for their pots after waiting a day. Emmett’s pot did weigh in at 92% of its original weight after a day, demonstrating shrinkage consistent with that of other groups. His pot also demonstrated, for the most part, a higher decrease in size than seen in Group A or B.

	Original measurements	After 1 day	Loss
weight (grams)	560 g	520 g	-40 grams
height (centimeters)	80 cm	70 cm	-10 cm
diameter–rim (centimeters)	17 cm	13 cm	-4 cm
diameter–widest part of pot(centimeters)	8.5 cm	8.5 cm	0
wall section (centimeters)	1.7 cm	1.9 cm	+2*

Group E’s pots, which used clay from the arb, tended to lose less weight, about 5-7%. Their pot making process was different from others, in that their clay came dry and they hydrated it themselves, so it is reasonable to expect greater variability in moisture, which could impact shrinkage. Below is Gisele’s data, which shows minimal shrinkage in terms of size and 94% mass retainment.

	Original	After 1 Day	Loss
Weight	543g	512g	32g
Height	7cm	6cm	1cm
Diameter (rim)	5cm	5cm	0cm
Diameter (widest)	11cm	11cm	0cm
Wall Section	9.85mm	8.01mm	1.84mm

Final Thoughts

There were some anomalies in the data reporting, probably due to unbalanced scales or the uneven thickness of pot walls and diameters, that led to some pots gaining weight and others gaining thickness or diameter. These anomalies are hard to interpret, since we can’t be sure whether they were caused by the materials we used or confounding variables like measurement errors. We will continue to take measurements as our pots keep drying, and hopefully, be able to move towards some more definitive conclusions.

While our pots have yet to be fired, we can still learn some things about the differences in tempers and clay used in Early Medieval England pottery. Despite several anomalies, there was about a 10% loss in weight across the pots using ‘industrial’ clay and added temper, whereas the arb clay had about half of that weight loss, about 5-6%. This could mean that more tempered clays could have a lower shrinkage rate, but we would need a larger sample size to confirm this, or to take later measurements. Most industrial clays that have a higher firing temperature have a higher shrinkage rate, whereas lower firing clays tend to have a lower shrinkage rate. The data we have collected confirms this, as the arb clay would not be fired at the same temperatures for the clay most of our groups used.