The age old question…how do I get rid of mold!

[medievalbard]

I know this has been asked thousands of times, but bear with me. I recently bought a very large undyed unfinished double butt piece of leather from Tandy. I usually work with pre-dyed, prefinished leathers, but I figured I’d take a risk and learn how to die and finish leather myself. However, an unexpected issue that has risen is that before I can even get to finishing/dying, mildew/mold begins to form on the belt on both sides, very soon after I finish stamping a design(I’m talking under an hour). What on earth do I do to make sure this doesn’t happen? This also happened with the same leather when I attempted to wet form leather around an AirPods case and when I clamped a piece of leather to make a key tray. The mold in question is little black spots, that don’t smell or feel strange, but are definitely very noticeable. Could it be because I soaked the leather overnight? I usually only soak it for an hour or two, but I had some extra time so I wanted to see if it’d make a difference. My basement is fairly low humidity, and I have a dehumidifier running constantly set to about 45%. I tried rubbing it with diluted alcohol, but that had little to no effect. I’d appreciate any and all ideas!

[SUP]

Spray diluted white vinegar on the leather. Wait a minute or two, then wipe off the excess  - do not allow it to soak in - and allow it to dry.  Condition well, once completely dry, preferably t least 24 hours later.

This has worked for me. 

[AlZilla]

There was a similar issue here maybe 6 months ago or more. The consensus was that some kind of metal fillings had contaminated the hide, if I recall correctly. The vendor replaced the hide.

That makes more sense than mold forming in an hour or two, I'd think. Even over night seems too quick for mold.

[bruce johnson]

Agree with AlZilla. Metal contamination. You can clear it with an acid treatment. The metal flakes interact with tannins in  the leather when it gets wet. Diluted lemon juice wiped on or oxalic acid. Most hardware stores sell oxalic acid as “wood bleach”. Dilute 1 teaspoon into a pint of water and sponge it on.

  The source of the metal can be anywhere from the tannery to your shop and tools. If you handle a steel tool and then wet leather sometimes that is enough to make specks or smudges. Particles falling off a tool can do it. 

[Northmount]

Definitely not mold.  If you do a search, you'll find this has come up a number of times and has been answered by me and others.  Can be very disheartening when it happens.  Oxalic acid (as Bruce says) is a good remedy, as long as there isn't a piece of iron/steel buried in leather, possibly from a band knife during a splitting operation.  Takes a little longer to show through than when it is on the surface.  Pattern was traced on and all the swivel knife work was done when it showed up the next morning.  It was in a 1" wide border area, else I may have been able to hide it with some tooling and dye or paint, especially if it was in the back grounding.

Search for blue, black gray spots.  It's the same process as vinegaroon.

 

[medievalbard]

Interesting! Metal contamination hadn’t even occurred to me. I use an arbor press for repeated stamps on some of my straps/belts, and the side of the wet form that had the specs was a side with a bare steel clamp, so that could definitely be it. Thank you all so much!

[SUP]

1 hour ago, AlZilla said:

That makes more sense than mold forming in an hour or two,

Oh it happens though. Mold grows so fast, it is eerie. My spray bottles all look alike and once, I picked up the water spray instead of the vinegar one. As I watched, the mold increased over the surface of the leather that I was treating. It was unpleasant, to say the least. Threw away that leather.

 

[Ferg]

I have an unrelated/related question for the OP. Why on earth are you soaking your leather overnight or longer?

Do you know how to "Temper" leather?

[medievalbard]

On 4/27/2025 at 7:34 PM, Ferg said:

I have an unrelated/related question for the OP. Why on earth are you soaking your leather overnight or longer?

Do you know how to "Temper" leather?

To be honest, no. I’ve learned that the best way to go about stamping/forming leather is soaking it in water(tap in my case) for a few hours or overnight. This has worked just fine for me up to now, but if tempering is easier or better, I’d love to learn how!

[AEBL]

Ok - I'm also fairly new compared to a lot of the more seasoned folks here, but this guy explained it in a way that made sense to me. I have been stamping and tooling leather using his advice and it has turned out sorta good. I think that "casing" leather was originally leaving it in a tray of water for a while (a case) overnight, or "a while" and then taking it out and letting it dry "to the right consistency."

Joe Meling wipes on water with a sponge and watches how quickly the water is absorbed. You may decide you like a different way, and it may turn out to work great for you, but definitely get out in the shop and see what works.
 

 

[Ferg]

2 hours ago, medievalbard said:

To be honest, no. I’ve learned that the best way to go about stamping/forming leather is soaking it in water(tap in my case) for a few hours or overnight. This has worked just fine for me up to now, but if tempering is easier or better, I’d love to learn how!

As I have said many times, "I have been at this a long time." There are probably as many ways to do this as there are folks trying.

That said: I run the tap water so it is moderately warm. I hold the leather under the faucet until there are no bubbles emitting from leather, turn it over to opposite side and do the same. Use an old terry cloth towel or old clean T-shirt laying it flat on table, lay the dampened leather on top of the cloth and roll the towel and leather together. Leave overnight. When you unroll it next day it will be damp and a little darker in color than when dry plus very pliable. Lay the leather out on your stone you use to engrave and stamp. Allow the leather to dry enough you can see it begin to change back to original color. It is ready to work. Naturally it will dry out as you work your stamping. Use a large cellulose sponge that is wet, not dripping, to go over the leather piece. This will replace some or most of the moisture you started with. Continue your carving or stamping.

When I am finished with the engrave I make sure the piece is laying flat and place the towel over it overnight. You can do what ever finish you wish at this time plus the leather will take an impression with a personalized stamp with ample pressure.

Hope this helps. Remember one very important thing. Take your time with casing the leather. Do it correctly and you will never regret your results.

Photo is of a piece I carved over 40 years ago after using above tempering method.

Ferg

[Ferg]

6 minutes ago, Ferg said:

As I have said many times, "I have been at this a long time." There are probably as many ways to do this as there are folks trying.

That said: I run the tap water so it is moderately warm. I hold the leather under the faucet until there are no bubbles emitting from leather, turn it over to opposite side and do the same. Use an old terry cloth towel or old clean T-shirt laying it flat on table, lay the dampened leather on top of the cloth and roll the towel and leather together. Leave overnight. When you unroll it next day it will be damp and a little darker in color than when dry plus very pliable. Lay the leather out on your stone you use to engrave and stamp. Allow the leather to dry enough you can see it begin to change back to original color. It is ready to work. Naturally it will dry out as you work your stamping. Use a large cellulose sponge that is wet, not dripping, to go over the leather piece. This will replace some or most of the moisture you started with. Continue your carving or stamping.

When I am finished with the engrave I make sure the piece is laying flat and place the towel over it overnight. You can do what ever finish you wish at this time plus the leather will take an impression with a personalized stamp with ample pressure.

Hope this helps. Remember one very important thing. Take your time with casing the leather. Do it correctly and you will never regret your results.

Photo is of a piece I carved over 40 years ago after using above tempering method.

Ferg

Another from the past: