Historically, the process of making gut music strings involved the use of various chemicals, some of which could be extremely toxic. The preparation of gut strings required several steps to clean, treat, and refine the material. While string-making details varied by region, here are some of the chemicals that have been historically used:

Alum: A compound containing aluminum, was used for its astringent properties. It could be applied to the gut to enhance certain characteristics.

Ammonia: Often derived from animal urine, ammonia was used for its alkaline properties in the cleaning and treatment of gut.

Arsenic: Arsenic compounds were sometimes used as a preservative to protect gut strings from decay and insect damage. While effective as a preservative, arsenic is highly toxic.

Borax: A naturally occurring mineral, borax was used for its cleaning and preserving properties. It helped to remove impurities and contributed to the overall treatment of gut.

Carbon Disulfide: An inorganic compound, CS₂ was used as a gasification agent to protect against pests, but the practice was discouraged due its foul-smelling nature and extreme flammability.

Copper Sulfate: Employed for its fungicidal and antimicrobial properties. It was used to protect gut strings from decay and deterioration during storage.

Lead Acetate: Also known as sugar of lead, led acetate was sometimes used in gut processing. However, lead compounds are toxic, and their use has been phased out due to health concerns.

Lime (calcium oxide; calcium hydroxide): Was often used in the initial stages of gut string preparation. It helped to remove flesh and other tissues from the intestines during the cleaning process.

Lye (sodium hydroxide; potassium hydroxide): Is a strong alkaline substance that has been historically used in the process of dehairing and cleaning gut. It helps break down and remove unwanted tissues from the intestine walls.

Mercury: Mercury was used in the treatment process to improve the flexibility and durability of gut strings. However, mercury is an extremely toxic substance, and its use in this context had health risks for those involved in the manufacturing process.

Potash (potassium carbonate): Typically derived from plant ashes, potash was another substance used in the processing of gut for musical strings. Potash was employed as an alkaline substance to help break down and remove unwanted tissues from the gut. It contributed to the cleaning and dehairing process, making the gut more suitable for string-making.

Saltpeter (potassium nitrate): Saltpeter was occasionally used in gut treatment for its preservative properties.

Shellac: A natural resin secreted by the lac bug, shellac was used as a coating for strings to enhance their durability and protect them from environmental factors.

Sulfuric Acid: Sulfuric acid was employed in the processing of gut strings to modify their properties, such as color and texture. It is a strong acid and needs to be handled with care due to its corrosive nature.

Wine Lees: The sediment left after the fermentation and aging of wine, were sometimes used in the gut string-making process. The acidic and tannic properties of wine lees helped to soften the gut and cleanse it, aiding in the removal of impurities and undesirable elements. The acidic nature of wine lees also contributed to the preservation of the gut material.

Zyklon B (hydrogen cyanide): In 1930s Germany, highly toxic hydrogen cyanide was recommended as a gasification agent in the storage and protection of gut strings against flies, bacon beetles, mice, weevils, moths, and other pests. "Anyone who does not have the opportunity to protect their stocks of dry goods from being eaten in the manner described above must shake and beat them thoroughly at least once a week during the months listed, because this deprives the pests of the rest they need to pupate and multiply." [Handbook for Intestines: Processing/Refining/Preservation/Artificial Casings. Gustav Raufmann. Berlin, 1939]

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It's crucial to note that the historical use of these chemicals was based on the knowledge and technology available at the time. Over the centuries, advancements in technology and increased awareness of health and environmental concerns have led to changes in string-making practices. Modern methods involve much more environmentally friendly and less toxic processes.