Metal finishing Q&As since 1989
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Info Requested on Muriatic Acid
Q. I have a large number of antique lock sets that have been subjected to many coats of paint of various types. Some have considerable rusting, I am trying to restore these to salable or usable condition.
I was informed by a firm that soaking in muriatic acid [affil links] would do the job as opposed to sulfuric acid.
Can you help? True or false and what proportions of water and acid?
William B. BallAntique Lock & Key - Calgary, Alberta, Canada
2001
A. Muriatic acid is diluted hydrochloric acid and will do the job fine. Read the warnings and directions on the container of acid and be careful using it. I'm not going to guess what concentration is best. You can find a material safety data sheet (MSDS) on this chemical at siri.org/msds/ which gives this info for free.
The acid attacks the finish and the base metal. However, once the base metal is exposed, the acid will promote rusting. Rinse off your part once the acid has done it's job, then apply whatever type of finish immediately afterwards. Hydrochloric acid is actually used in metal finishing as a cleaning/etching agent right before the finish is applied. You may want to try this out on something similar but less valuable first.
You might also want to try a product called C-L-R [on eBay or Amazon] which is designed to dissolve calcium, lime, and rust deposits. This might be cheaper and/or provide better results.
Tim Neveau
Rochester Hills, Michigan
A. Sir,
Muriatic Acid, approximately 31% hydrochloric acid by weight, is too strong to use directly on an assembly. If used directly on a single part, a brush may be used to wipe away the dissolved rust so that the acid may attack the layers below. The acid will remove rust many time faster than clean metal however, in an assembly, you might do serious damage to small parts with strait muriatic acid. If you must, "soak" an assembly. Dilute muriatic acid 20 to 1 and soak for 24 hours. After soaking, rinse thoroughly with hot water and brush if possible. Never never never use sulfuric acid. The last process should be lots of soap and hot water with a brush if possible. Dry with forced hot air, I use my wife's hair dryer [on eBay or Amazon], and apply a surface protectant.
Note; Muriatic Acid causes very painful burns that are not noticeable until the damage is done. Wear protective rubber gloves [on eBay or Amazon] and eye protection (goggles [on eBay or Amazon]). Also, use in a well ventilated area as the fumes are harmful.
Norman B. Czerski- Eagle River, Alaska
2003
Q. Most I know about making sulfuric acid is you can get it out of lithium batteries - but that is not exactly something you really want to do and is expensive. Regarding the stuff I read about hydrochloric acid..yes its muriatic acid and there is no need to make it, it is a pain though to try to buy it these days, its not as commonly sold as it used to be in the hardware stores and getting it online is also not easy. However, I found a website and ordered HCl 37%, reagents.. anyone expand on that for me? is that stronger or weaker than the grade of muriatic acid from hardware store..
Amistudent - NY, New York
2004
Ed. note: You can get muriatic acid [affil links] by clicking on the link, but it's still available in stores as well. It's about 28 percent HCl. Consumers can get reagent grade sulfuric acid [affil links] on-line.
As previously noted, consumers would be much better off working with commercial household products than using these dangerous acids, which were designed for professional use by trained personnel, for purposes they weren't intended.
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