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MOULD STAINING IN VEG TAN

Hi Phil

I have been making knife sheaths, I wet the leather then vacuum shrink it to the blade using a food vacuum bagging machine. This gets the sheath to conform to the knife and holds it in when the leather dries hard.

I notice the leather quite quickly starts to develop a bit of greyish mould staining. However, it doesn't seem to do this if it has been dyed previously.

What, if anything can be done to stop this?

Regards

Bruce

5 comments

5 Comments

elizabeth

May 03, 2023

Hi Bruce, I have also experienced mould spots (that don't come out easily) when wetting undyed leather. I see Phil's response and recognize this could be from metals in the tap water and also wetting the leather for too long. I will try distilled water and less time soaking, quicker to a dry environment.

Leathercraft Masterclass

May 03, 2023

Hi Bruce,

Genius idea by the way!

Is there any chance that you have a picture of the staining? There could be a number of reasons, so I will come up with a few wild guesses off the top of my head:

- The leather is reacting with the carbon steel blade somehow (if it's not wrapped).

- There are metal deposits on the leather causing it to oxidise with prolonged moisture exposure (are you making the knives too?).

- The plastic bag is reacting with the leather somehow.

- The tannins in the leather are reacting to being wet for too long without being able to dry out.

- The water you are using contains high levels of metal (tap water?) which are reacting with the tannins (lead, copper, iron etc). Maybe try distilled water?

I have moved this question to the 'Help From The Community' section as the Mastermind Group is for course specific content.

Keep us updated.

bruce

May 03, 2023

Replying to

Thanks Phil. I will get some pix tomorrow and reply more fully.

bruce

May 11, 2023

Replying to

Back again. Well, as is always the way, I couldn't reproduce this effect at all. I note your comments Phil, about water mineral content etc. However, we are on rain water here and it's filtered so doubt there is anything in it to cause mould growth.

From memory it always seemed to be under the wood when clamping the leather into a shape while wet. It could be something about the leather as it is inconsistent as to when it happens. Or could be fine metal dust contamination in my workshop from knife making.

I will attach a couple of photos in which there is definite staining. However, in this case it was caused by the carbon steel blade inside. This set up was a trial run mock up for a dirk I am building as I needed to get sizes and a pattern worked out for the leather plus the stitching and process to get it all to go together. So, not worried about the rust bloom coming through as it will end up in the scrap bin anyway.

But, as you say, when wet moulding a sheath to a blade it is always wise to wrap it in several layers of cling film or coat in vaseline, or both.

As a tip on vacuum moulding, the leather wont dry in there because it's a vacuum. So once the leather has pulled into the desired shape, release the vacuum and remove from bag to dry. But don't remove the blade or other former being used until the leather is dry.

I also find that the internal pattern on the vacuum bag (that allows the bag to evacuate the air) will imprint a pattern on the leather. If that is not desired, then I cut a piece of thick polythene and place it between that side of the bag and the leather. I use what we call in NZ, builders plastic: a thick black plastic used under concrete etc to block water and rising damp. It's smooth and also very useful to stop clamps and blocks etc sticking to the work when glueing up as PVA and epoxy wont stick to it.

Probably those thick plastic document sleeves will serve the same purpose.