Connect the Dots: Hemlocks and 19th Century Tanneries

Published by the Vermont Community Newspaper Group in The Shelburne News and The Other Paper, 10/6/22

How fitting to be surrounded by hemlocks, I thought as I scrambled down the steep bank of the brook. Hemlocks were one of the key elements in the 19th-century mill I was exploring and here were some of their descendants as witnesses. Would I find any remnants of the old dam or the foundation of the water-powered bark mill? I continued downslope to see.

The old bark mill was part of the local tannery that operated from the early 1800s to the 1880s processing animal hides into leather. After the saw mills and grist mills creating materials for shelter and basic foodstuffs, the tanneries were the next most important local industry supporting early European settlers. Without shoes and boots for people, or harnesses and saddles for horses, farming life would have been very difficult in the era before plastics, rubber, and gas-powered vehicles.

Transforming animal skin into leather was a skilled, labor-intensive, multi-step process that used a sequence of salt, lime, and tannin treatments with large amounts of water. Tannins are natural chemicals produced by many plants to deter pests (they also give coffee and tea their color and astringency). Tannins in a water solution will chemically bind to the animal skin proteins and alter them to keep them from decaying. Tannins also make the skins more durable, water and heat resistant, and flexible. Hemlocks have large amounts of tannin in their bark, and are common in Vermont, so tanners here used them extensively. The hemlock bark needed to be ground to a powder so the tannins would easily dissolve in water. 

The tannery site I was looking for was on several 19th-century maps, and had all the key environmental features together in one place. To produce the power needed, it was built below a steep section of brook created by a geologic fault line. The tanner built a dam to impound the flowing water and regulate its flow to the bark mill. The water power turned the bark mill’s grindstones to grind the bark into powder, much like a grist mill’s grindstones grind wheat seeds into flour. Of Vermont’s 126 bark mills in 1850, three-quarters were water-powered, with most of the rest horse-powered. The brook’s steady flow of water was also essential to processing hides because many of the steps required chemical solutions soaking in large vats, and rinsing with large amounts of water.

Tanners gathered the materials they needed locally. Farmers brought hides in from their livestock, often paying the tanner with a portion of the hides. Wood lot owners provided hemlock bark, and lime came from the limestone quarries common in the Champlain Valley.  

The tanner’s process began by salting the skins to stop bacterial growth, then rinsing the salt out with water. This was followed by soaking the hides in a lime solution to remove the hair and any fats left, then de-liming them with either water or a vinegar solution. Finally, the hides were put to soak in a series of water vats with increasing concentrations of dissolved tannins.  Hides were moved from vat to vat as determined by the skill of the craftsman over many months to become fully cured leather. The tanning process was known to be very smelly, and the waste was usually disposed of in the brook. 

Cobblers and harness shops bought most of the finished leather. In the end, the community was shod and had the harnesses for horse-drawn farm work.

Later in the 19th century, bark tanning was eventually displaced by a synthetic tanning process using chromium salts, which took only hours to produce finished leather instead of months. Bark tanneries eventually closed.

I looked around the site to see what was left of the 19th-century mill works. Upstream, I could see the remnants of a grist mill and saw mill, but there was little evidence left at the tannery site. Some stonework seemed to line up on both sides of the brook, but it was heavily damaged. Probably the floods through the narrow valley over decades had flushed much of it out, leaving me to imagine the rest from the descriptions.   

It was time for me to head back up the steep ravine, and I steadied my ascent by holding onto the 2-foot diameter hemlock trunks. I paused for a moment to catch my breath, and because the hemlocks’ dense shade keeps out understory growth, I was able to review the valley below. All the pieces had come together here: the geology of the steep ravine creating the opportunity for power, and the rushing water to drive the bark mill, to soak the hides, and take away the refuse. But without the gray, platy hemlock bark under my hands, none of this would have been possible.

Copyright 2022 Jane Dorney