#WednesdayWisdom: When To Use Alum

Anyone who has had a screw break off inside a post, or a flat spring screw break off in a key, knows how frustrating it can be.  If you’ve come across a horn that has had flood damage of any sort where the screws and rods are rusted and corroded and nearly everything seems frozen, you may have wondered if it’s worth the trouble.  However, you are just one chemical reaction away from success and we’ve got a couple tips on how to use alum to quickly corrode hardened steel without damaging brass.

You may be familiar with alum from making pickles, but we’ll use the cheaper non-food grade alum for these tasks because it’s much more affordable and we don’t plan on using it for pickling!

After hurricane Katrina, we saw lots of horns with rusted pivots and rods.  When the usual fixes of penetrating oil, heat, and light tapping wouldn’t loosen the screws, we sometimes had to put alum to work.

There are a couple common reasons why some people claim alum doesn’t work, but there’s a reason for it.

Concentration: dissolve one pound alum in 4 quarts of water- less than this will not give you the necessary reaction

Aluminum Pan: you can only use a pure aluminum pan for this reaction to work

Heat: it needs to be at a boisterous simmer

Time: check every 30 minutes, but many projects will need several hours

Hardened but not stainless: stainless steel will not corrode or dissolve in alum

If you have all of these elements, it WILL work.

  1. Dissolve one pound of alum in 4 quarts of purified or distilled water in a large aluminum pot.  This may seem like a lot, but you can save it and keep using it many times over.
  2. Bring alum to a boil and then reduce to a simmer. Suspend your part so that it is fully submerged in the water.  Keep in mind that steam and boiling water will damage lacquer, and potentially other finishes, so you may want to test on a spare part if that will affect your outcome.
  3. The part should bubble when you submerge it, which will clue you in to the fact that there is a reaction occurring.  
  4. Check every 30 minutes, and poke at the screw or stuck steel to see if it has corroded to the point of being softer and able to be removed.  Add water as necessary to keep part fully submerged.
  5. Once you’ve achieved success, don’t throw out your alum solution!  Keep the pot out for the water to evaporate, leaving just the alum behind.  Next time you have a stuck part, just add purified water to your aluminum pan to reconstitute.

We’ve used the same alum solution for a long time now- many years and many parts.  We’ve even heard store of people using big aluminum turkey fryer pans and submerging the entire instrument!  This is primarily a technician’s solution, as you may have to unsolder a post, use the alum, clean the post, and then re-solder, but can be used by anyone with the right equipment.

We recommend not using this technique with roller keys with stuck rollers, as it can damage both pearl rollers and plastic rollers. Should your roller screw be stuck beyond what oil and time can help with, you may need to use a jeweler’s saw to cut the screw, freeing the roller, and then submerge the key with the remnants of the roller screw in alum to finish the job.

MusicMedic Products Used

Deluxe Jeweler’s Saw Blades

Happy repairing!