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Japanning is an age old process of protecting metal surfaces by applying several successive layers of a syrup-like black coating and then baking it to a hard and durable finish. It was often applied to vintage machines and tools before the advent of petrochemical based coatings. Although there's debate on its exact recipe among vintage machine restorers, the coating was made by dissolving crushed, or powdered ashphaltum (bitumen) in turpentine and then combining it with boiled linseed oil.

While turpentine is a fairly good solvent for ashphaltum, it doesn't fully dissolve it, leaving large sized particulates suspended in the mixture. Getting decent results requires allowing the large particles to settle to the bottom over several hours and then filtering it. Even when filtered, it still tends to clump in regions when applied and doesn't consistently produce the highly-prized smooth satiny finish.

I suggested using acetone as an alternative solvent to another restorer, but he claimed the Ashphaltum only stayed in solution for 30 minutes before settling to the bottom, while turpentine action was faster. I'm surprised since acetone is very good at dissolving greases, oil, waxes and other organic substances. Why would it be less effective than turpentine?

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My question is what is in the "ashphaltum". I am a metallurgist but the materials section at Amoco also included the asphalt experts; Amoco did more R&D on asphalt pavements than any other oil company. I heard many times that asphalt is a blend of asphaltenes , resins , and oils , giving a wide variety of properties . Asphalt is fully soluble in acetone, I believe they usually used MEK to clean lab equipment. So if it won't dissolve, your material is not all asphalt.

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  • $\begingroup$ Thanks. It could be that acetone may be an excellent solvent, but isn't good at forming a suspension with certain materials? Oil doesn't dissolve in water, but it can be suspended in water. Milk is an example. Does the polarity of acetone or higher density of the ashphaltum make it difficult for acetone to hold it in suspension? $\endgroup$
    – user148298
    Feb 8, 2022 at 2:45

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