I really can’t recommend hydrochloric acid for this use. Sure it works, but it’s also good at causing rust on everything else around. A safer choice would be sodium citrate: https://www.youtube.com/watch?t=1&v=fVYZmeReKKY

There you have it. And yes, it’s the vapors. Hydrochloric acid is quite volatile and will leak out of any container. In old laboratories it was always easy to see where the acids where stored, anything metal around it was always corroded.

To the moderators, Are all my postings subject to Moderation? Wearing thin when trying to give sensible answers quickly

Ian

does no one use evaporust?

On 7 June 2025 at 22:05 Sonic Escape Said:

…

And can’t the residual chlorine be neutralized with something?

Not cheaply!  A microscope reveals even highly polished metal-surfaces are pitted and scratched, leaving plenty of space for micro-contamination.  Cleaning Hydrochoric Acid residues needs a penetrating chemical that dissolves deeply embedded molecules.  I guess the object would have to sprayed in a vacuum chamber and then boiled in a bath.   A complicated expensive process, not put together using bits and bobs sold by Lidl!

Ferric Chloride is corrosive enough to dissolve Copper – it’s used to make printed circuit boards! Rust removing Sulphuric Acid leaves much less corrosive residues and they can mostly be washed out with water.    Always dangerous to say never, but industry don’t use Hydrochloric Acid as a rust remover.  And Sulphuric Acid isn’t idiot proof – concentration and time both matter.

Though Model Engineers often like chemical folk remedies, they rarely compete well with properly tested professional products.

Another example.   Molasses is often recommended as a rust remover, and it might work well.  Certainly doesn’t have serious unwanted side-effects!  Unfortunately molasses exists in many different forms, it isn’t a single well-defined product that always does a good job removing rust.  The stuff sold in the UK for cookery is too expensive and refined to remove rust.   Cattle feed molasses works, or not, depending on the sugar refining process used to make it.   As does the stuff sold for horses.   Hit and miss, try it and see.

For removing rust, it seems crude acidic molasses of the cheapest possible kind is best, but that variety is probably only available where sugar is made from cane rather than beet.  Texas, not Norfolk!   And because crude molasses is likely to be processed depending on industrial needs, what Joe Public gets as “Molasses”  s a gamble.   So recommending molasses for rust removal is unreliable, unless it’s explained where others can buy the same one.

Good fun experimenting with potions though – just don’t jump too quickly to conclusions.

Dave

The Backyard Balistics formula is basically make your own monosodium citrate. This is a recognised chelation agent. You can buy monosodium citrate (E331 food additive) for les than the ingredients used for making your own. I don’t know if a little bit of free citric acid helps with the diy method.

Robert.

remember to de-grease first or you get patchy results. Store outside in child and pet proof box.

Citric acid is normally available as dishwasher and kettle descaler. You don’t need food grade and it is safe to handle and use in the kitchen or near children. It is sometimes suggested that you ‘damp it down’ by adding washing soda (calcium carbonate) to make a buffered solution. NOT caustic soda – drain cleaner- as it aggressively attacks skin.

For electrolysis mentioned above use washing soda NOT caustic soda.

Phosphoric acid is the best amateur cheap compromise. It can be used quite weak and apply by brush not dunking for best economy. After 5-20 minutes wash it off  or leave for hours and it produces a crusty deposit and stains the workpiece but can be re-cleaned. It is available as swimming pool neutraliser and is hand safe in those formulations. Often the suppliers are resellers watering it down for more profit. My quick access jar actually keeps increasing in contents as it absorbs moisture. The dilution doesn’t seem to matter.
Sometimes Cocacola is suggested – this is because it used to contain phosphoric acid.

These agents are not a substitute for elbow grease – you must make the effort to remove all rust you can first.

After washing and drying on a good job you will see it quickly (2-5 minutes) darken as a fine new rust film forms. So as wuick a possible treat with well diluted clear Waxoyle car underbody treatment. This is much more user friendly than oil. Also soft candle wax (not car polish) can be used on hand and woodworking tools.

I bought my last bottle of citric acid in an ordinary chain household emporium without question!

It is effective, too. Not ever so fast and you do need remove as much rust first by, e.g. wire-brush, then degrease the workpiece.

My last use for it was cleaning some neglected taps and dies I had recovered.

Bazyle,

I suggest you view the Backyard Balistics youtube video linked to earlier.  Adding Sodium in the form of carbonate, bicarbonate or hydroxide doen’t “damp down” the citric acid. It converts it to monosodium citrate. This is a different chemical and removes rust by chelation.
Use of plain phosphoric acid requires great care as it will consume the base metal. The commercial phosphoric acid based rust converters include corrosion inhibitors to prevent this in normal use.

Robert.