Since the days of the Roman empire, alum was used as a mordant or fixative that allowed textiles to be colored using vegetable dyes.
Initially imported from Italy where there was a Papal monopoly on the industry, the supply to Great Britain was cut off during the Reformation in England.
In response to this need, during the 16th century, Thomas Challoner found that fossils in shale along the Yorkshire coast were the same as those found in alum producing areas of Italy and Europe and, as a result, an alum producing industry was established in the region.
Alum was made, in part, from extracting shale, then burning mounds of it for up to nine months. The large scale and complicated process involved extracting then burning huge piles of shale for months, before transferring it to leaching pits to extract an aluminium sulphate liquor.
The process of creating alum involved mixing leachate with aged human urine to provide ammonium, and roasted kelp for potassium. At the peak of alum production the industry required 200 tonnes of urine every year, equivalent to the produce of 1,000 people. The demand was such that it was imported from London and Newcastle, buckets were left on street corners for collection and reportedly public toilets were built in Hull in order to supply the alum works.
This unsavoury liquor was left until the alum crystals settled out, ready to be removed. An intriguing method was employed to judge when the optimum amount of alum had been extracted from the liquor: when it was ready, an egg could be floated in the solution.
It was also said that barrels of urine also came from as far away by boat and were hauled up the cliff by a tramway, that was also used to lower barrels of alum down to the boats.
The alum industry began to slowly decline around the mid 19th century when synthetic alum became available in 1855 and, when eventually aniline dyes were invented a few years later, the mordant was no longer required. The last alum works in the region closed around 1871.
There are many sites along the Yorkshire Coast which bear evidence of the alum industry. These include Loftus Alum Quarries where the cliff profile is drastically changed by extraction and huge shale tips remain. Further South are the Ravenscar Alum Works, which is one of the best-preserved remnants of this once important industry.
The site is under the protection of the National Trust and around are interesting information boards that explain the ruins and the process of creating alum.
Images from web – Google Research