THE TANNING PROCESS

       When the hides first arrived at the tannery, the process began with washing the hides in water to remove dirt, blood, manure, and other matter. This process usually required flowing water to thoroughly clean the hides.

        Chemicals were an important component of the tanning process and three agents were used in abundance. The first agent was lime. The hides were soaked in a lime/water solution in vats that lime worked to soften the skin and swell it in order to loosen the hair follicles so they can be removed. Each vat would contain a different solution of lime, and more lime would have to be added periodically to ensure the solution was strong enough.  For the most part, Unity tannery used lime that came from quarries in Rockland.  The second agent used was the mastering solution. This was a vile solution of water, salt, and dung; usually from chickens, pigeons, or dogs. Horse and cow dung was not used in the solution because of its weaker potency. The mastering solution removed proteins from the hides in order to halt decay. In addition, it was also used to soften the hides of cows and calves. It was here that after being cleaned and all of the hair removed, the hides were placed in bating vats to neutralize the lime. Bating vats contained salt, water, and chicken or dog manure. The tanner would then wash the hides thoroughly in clean water.  After the liming process the hides were drained of the lime solution and then the tanner would place the hide on a sloping beam or bench and scrape off the remaining hair and excess flesh. This process was known as beaming. To do this the worker used a series of downward strokes using a dull beaming knife. An average beamsman could process a dozen hides a day.  Acid baths were used for the second step of tanning for only the toughest boar and ox hides. The acid was composed of heavily fermented rye and barley, essentially a very strong whiskey mash.  Like the mastering solution, it was designed to deteriorate proteins in the hides.

         The last step/process involved the tannin solution itself. Hemlock tree bark was ground into a pulp and then allowed to “bleed” tannic acids into the water. The astringency of tannin essentially halted the decay of the hides, closing the pores of the hide, therefore sealing it and preventing bacteria from breaking it down. Each required twice its weight in bark plus twelve gallons of water. The bark and water produce tannin, which slowly penetrated the hides and transformed them into leather. For superior leather, the tanner soaked the hides in a solution of water and bark for up to twelve to eighteen months. The tanning time varied greatly depending on strength of the tannin solution, thickness and density of hides, and the climate of the area.

         From this point, the hides were carried into drying rooms or lofts where the workers would pound the hides with mallets to make them more flexible or rolled using machines to remove all the traces of the tanning solution. The hides were then hung, usually in special drying rooms, to ensure drying in a fixed amount of time. Heavy leather for shoe soles or harnesses were only rubbed with oil so they would not become too flexible, while lighter leather was stretched, beaten, and kneaded. Other oils were used to make it soft and supple. Finally workers rubbed the lighter leather with a stone to bring out the desired grain and structure. Once these processes were done and the hides were dried, they were ready for shipping from the tannery. “Currying” also took place, a process in which the leather was shaped and thinned even further to make it more attractive and usable. However, it is not likely that the Unity tannery did this because their main production was sole leather that did not need to be as highly treated.

           The main fuel used for the tanning of hides in the Unity tannery was wood. Wood was brought in to burn, to create heat for the steam engine that ran the bark grinder, and the rolling machines. Most of the other tasks at the tannery were done by hand and didn’t require the use of fuels.

             It could be assumed that a tanner did not need to have many special skills to tan, and every tanner did all parts of the tanning process. Also, the tanning process could have been done during spring, summer, and fall due to a possible frozen river during winter months.