From Mugs to Solo Cups: Understanding Capacity in the Archaeological Record

By Eleanor Breen / Project Manager, Archaeological Collections Online

Some of you out there undoubtedly enjoyed a beer while watching the Superbowl this past weekend.  Stop to consider – did you drink your beverage out of the can or bottle?  Perhaps poured it into a red Solo cup (that emblem of modern America material culture recently immortalized into a country song) or, if you’re more high brow, a frosty mug?  In the eighteenth century, beers and ales were often consumed from straight-sided mugs whose capacity, or the amount of liquid held in each cup, grew increasingly diverse over time.

Nottingham mug missing its base making it impossible to measure its true capacity. Based on the measurable rim diameter of 70mm, it may have been in the half-pint range.

So the question is, how can we get at capacity in the archaeological record?  Let’s all take a trip back in time to middle school math when we learned important principles of geometry like volume.  An 18th-century mug is basically the same shape as a cylinder.  If we can remember the equation for the volume of a cylinder (with the help of Wikipedia), we should be able to measure the volume of the mugs and then convert that to capacity (pints, quarts, etc.).

Our minimum vessel countfor the mugs from the South Grove midden is 39.  However, only 9 of these have the measurements necessary to solve for volume – rim or base diameter and height.  Most of these are made of Nottingham stoneware.

 

These steps were taken to find volume and create table 1:

1) Volume = πr2h

2) To get the radius, we divide the rim diameter by 2 and then square the number.

3) Then we plug our numbers into the equation and get a volume in mm3.

4) Here, the numbers start to get a little unwieldy.  To simplify, I converted mm3 to in3.  This was done by dividing the volume in mm3 by 16390.

5) Finally, the volume in3 needs to be understood in terms of a system of liquid measure and was converted to the UK pint by multiplying in3 by 0.03.

6) Sources like David Wondrich’s (2010) Punch: The Delights (and Dangers) of the Flowing Bowl tell us the following:

4 to 5 ounces = 1 gill or quartern

4 gills or quarterns = 1 pint

2 pints = 1 quart

2 quarts = 1 pottle

2 pottles = 1 gallon

Evident in the capacity column is, well, some inconsistencies.  None of the capacities are exact.  If we try to fit them into the standard capacities listed in Step 7, it appears that a pint might range in actuality from 0.82 to 1.37 pints, depending on how you round.  Assuming all our measurements are correct, we’re left to explore the potential explanations for these discrepancies.  As David Wondrich (2010:98) warns us, “…a gallon is not always a gallon nor a quart a quart.  It depends, you see, on what you’re measuring and when and where you’re doing it.”

Table 1

And coming soon… Part 2 of this capacity blog post where we explore related studies in archaeology and the cultural significance of capacity research!

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