How can I tell if leather is vegetable tanned?

Question

In my continued effort to learn more about sharpening I see that the last step always involves stropping. Purchasing one seemed folly as someone mentioned that

woodworkers who buy strops should hand in their woodworking cards

When it came to leather selection it would mostly come down to availability since I had no intention of buying a strop. Unanimously people have suggested that if I used vegetable tanned that I do not have to treat it with something like chromium oxide before I use it.

That got me thinking: I have plenty of leather from previous projects. How do I identify a piece of leather as vegetable tanned vs. the most popular chrome tanned? Colour used to be a tell tale sign but with all the dyes available that is no longer a perfect guide.

Answer 1

The differing properties of vegetable-tanned hide over chromium-tanned is an interesting subject to read up on but I think it should be stressed here that a preference for one over the other for strops can be considered irrelevant, for multiple reasons.

Traditionalists often consider this a heresy and heated debates arise over it (particularly on straight-razor and knife forums it seems) with die-hard users insisting that veg-tanned horse butt is and always has been the best strop material going and anybody who says otherwise is not to be listened to, or something along those lines :-)

This is one of many points of contention that contribute to the high noise:signal ratio surrounding sharpening.

Because of this it's very easy to get bogged down in esoteric points like do I have to have veg-tanned leather? Should it be horse butt, or is bull neck leather better like someone else said? Or should I listen to those guys now promoting buffalo hide as THE strop material, better than anything that came before?

All of that is irrelevant if you just focus on results. Does your strop do what you want: remove a microscopic burr (also called a wire edge) and/or polish your edge? And does it do it efficiently?* If so that's all that matters.

And here is where stropping compound becomes obvious as the key factor. It is the stropping compound that does almost all of the work.

So not only does the type of leather not need to matter, you don't need leather at all. A few woodworkers today use strops just made from MDF or harder woods like maple with the stropping compound loaded onto the surface, and in head-to-head tests of denim-faced strops with leather-faced strops denim seems to do the job just as well. And for most of us denim scraps of large size can be had for free, which can't be said for vegetable-tanned leather.

*By efficiently I mean in perhaps 30 seconds, not the many minutes some people spend stropping razors on bare leather strops. We don't have time for that, we have wood to get back to.

Answer 2

So you found some scrap of leather from a manufacturer or some clothing (like a belt).

The trouble can come from leather, that has been processed using vegetable tannins, but that was previously chromed tanned and reprocessed.

Assuming that you can't get that information from wherever you are acquiring the leather or you want to verify the sources authenticity you have two simple tests at your disposal.

Burn/Ash Test

While both tests here are simple this one has the smallest time involvement. In an open air environment take a small strip or piece and bring it close to flame. Vegetable tanned leather should take longer to burn and when it does turn black/grey. Chrome tanned leather should have a bluish greenish colour when burned. The colour comes from the reaction of the chromium in the leather.

A source as a simple reference would come from Carryology.com where half way down the article the burn test is mentioned.

Boil Test

Another simple test is to put a thin strip of the material into a pot of boiling water. 100% veg tanned leather will curl up instantaneously. Chrome leather will just float in place. While both will go limp, chrome leather will not have the same initial reaction as veg. A video about the self-proclaimed the "Siegel Effect" shows the test in action. I stress self-proclaimed as this test has been used for quite some time before this video was released.

In the picture above there are two strips of leather in the pot. The one "on top" is confirmed vegetable tanned as it curled up when it was place in the pot. The second strip was known chrome tanned leather that just went limp and did not curl in nearly the same was as the other strip.

An article on the manufacturing of leather supports up this test by stating:

a normal vegetable tanned leather shrinks in water above 70ºC

In Conclusion

While both of the test are not perfect they are both easy indicators. It is worth noting there are other tanning processes in used but chrome tanned is the most widely used.

Aside from stopping, vegetable tanned leather is also sought after for making holsters and covers for axes and other tools (So as to not have a reaction with the metal). That could be another source to consider or another motivation to perform the tests.