'Witches' brew' works wonders on rust

By Kevin Ball editorial@age.co.nz -
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Murray Campbell fits a treated bolt to a door. An untreated hinge lies across the job. PHOTO/SUPPLIED
Murray Campbell fits a treated bolt to a door. An untreated hinge lies across the job. PHOTO/SUPPLIED

A "witchy poo brew" dating back hundreds of years and with associations to the slave trade is part of the latest project taking shape at the Henley Men's Shed.

Chairman Murray Campbell is putting together a set of display doors from recycled timber from a Wairarapa shearing shed. He planned to use the ornate and very old handmade hinges that came with the material. They were quite heavily rusted and he wanted to retain the original patina without using destructive polishing methods.

So he put them into a molasses bath, something craftsmen and engineers have used for hundreds of years. They emerged clean as a whistle, so clean in fact that after just a couple of minutes they took on the orange hue that indicated oxidation had begun again. A quick spray with WD40 stopped that and the hinges were ready to be fitted.

The mixture is non-polluting and non-toxic, so can be tipped out on to the lawn after use.

I first came across molasses baths some years ago when talking with veteran car restorer Barry Gillum, who's been using molasses for more than 20 years on car parts. But it goes way back beyond that. Murray's unsure of the origins but suspects it came about accidentally when somebody working at a sugar refinery dropped rusty iron into a puddle containing molasses and water.

Molasses, of course, is a product of cane sugar and is processed into rum, which at one time was a frequent method of payment for slaves. It's as cheap as chips -- $20 will get you five litres of blackstrap molasses from any firm selling stock food additives.

The molasses-to-water ratio seems to range from 1:3 to 1:10. Parts need to be clean of oil and grease before treatment so the liquid can come in direct contact with rust. There is no need for cleaning off rust scale as the mixture will dissolve it. The more rust, the longer it needs to stay in the bath. Light to moderate rust seems to be removed in about two weeks.

Don't use it on aluminium, though. One online correspondent reports that a chap used a 44gal drum as the mixture container. "It was the top half of the drum and the molasses mixture ate away the aluminium bung in about three days," he said.

The cleaning process is known as chelation and a version of it has been used in medicine for many years as a treatment for mercury and lead poisoning -- with chemicals, not molasses, obviously. An old boss of mine, former Times-Age editor the late Jack Brown, used to have chelation regularly as a treatment for heart disease.

Just as the molasses mix dissolves rust, the medical version dissolves the calcium in the plaque that clogs arteries, causing strokes and heart disease. Jack swore by chelation -- just as the blokes at the Men's Shed admire the effect of the molasses mix on iron.

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