Leather shrinkage in your projects

[fredk]

I've mentioned before about leather shrinking whilst making projects and I think some people didn't believe me

In this, all leather was cut from the same hide and the examples are actually from places close to each other

I've been making 60 of these key-ring coin purses;

I use an acrylic template (at top in picture) to draw around then I cut out the shape. The surface of the leather is dampened then a design stamp is pressed into the leather, (at bottom of the photo)

The cut and stamped piece on top of the template, matches up ok, its the angle the photo was taken makes it look like they don't align

Now here are two cut pieces, stamped then dyed with blue oil based dye

Can you see the difference? I've aligned each piece on the centre . Both pieces are now shorter than the template and slightly narrower

Close ups of each end;

These examples are amongst the most extreme but other pieces are also shorter. It doesn't matter if I use oil or acrylic dye, the leather shrinks in both length and width.

So what about thickness?

The hide, in the area where these pieces were cut from measures 1.05mm thick

After stamping but before dyeing the thickness is 0.89mm

and the blue pieces, and others, after stamping, dyeing and sealing are 0.75mm thick

A shrinkage of 0.3mm in thickness

It doesn't sound very much but if you are (or I am) making a case where a good fit is essential it may make the difference

Many years ago when I made certain types of cases I made them to be a very exact fit and could never figure out why that after stamping and dying the cases were too small. I thought I'd made some errors and often I made those cases two or three times over, the last being made over size. Then I realized that the leather was shrinking. 

I now take the shrinkage into consideration and sometimes rely on it happening in projects

Not all leathers shrink by noticeable amounts, some by more than others. I made someone a waist belt using top dollar leather. By the time I'd finished the belt leather had shrunk by almost 3/4 inch over a 42 inch length - but I was allowing for some shrinkage, so all was good

So I'd suggest if you are making a case or something which has a critical or exact size check your leather to see how much it will shrink

 

HTH

 

 

 

 

 

 

[Tugadude]

I totally believe you and have seen it happen in my own projects.  Until, that is, I decided to never, ever dye leather after cutting.  When I stopped doing that, I never encountered a problem.  

The other side effect of the shrinkage can be a loss of flexibility.  The leather becomes stiffer because some of the oils in the leather bond with the water molecules and when the water dries out, guess what?  The oils go along for the ride.  Less oil left in the leather results in stiffer leather.  I applied dye to some wallet pockets once, after cutting and not only did they shrink, they also became stiff as cardboard.  Sometimes that's OK, or even helpful, but not for what I wanted.

You can control at least some of the issues by dyeing the leather and letting it completely dry before cutting.  And if you are going to add some oil-based products later on, that probably won't have as big of an impact as water-based would.  

It is not uncommon for folks who own leather jackets to find that after a rainstorm that perfect fit now has to be handed off to someone smaller.

Just part of the deal.  Leather does what it does.

[Klara]

I wonder whether (some) leather might be stretched during tanning? Or maybe splitting - most leather we work with is split, isn't it? And then with humidity it relaxes back into its original shape. Sounds rather normal to me - wool does it all the time.

[Tugadude]

1 hour ago, Klara said:

I wonder whether (some) leather might be stretched during tanning? Or maybe splitting - most leather we work with is split, isn't it? And then with humidity it relaxes back into its original shape. Sounds rather normal to me - wool does it all the time.

I've no doubt that leather stretches during the tanning process.  I've seen wet hides hanging and they are quite heavy.  They have to be stretching.

[doubleh]

Since all the leatherwork I do is tooled expansion is what I get. The only thing I ever dye is a holster and I don't know if it causes them to shrink or not as they get dunked in water and then a saran wrapped gun shoved down in them and let dry.

[Klara]

14 hours ago, Tugadude said:

They have to be stretching

Then the question is solved for me

[Tugadude]

In 'Leatherwork Manual by Al Stohlman', Mr. Stohlman says the following:

"The modern tannery is made up of three major sections.  The first section stores, cleans and removes hair from the animal skins.  Next, natural oils are removed and preservative chemicals introduced into the very heart of the skin structure.  During the final stages of production the skin is stretched and dried."

So no need to take my word for it.

[chuck123wapati]

yup you cant tan hide without stretching it. When we tan( my son and I) we can almost double the size of a hide by stretching it on a frame and BTW that's what those funny square clamp marks are on the edges of hides you buy. They are stretching clamps!! The process known as tanning simply takes out the mucus and  some of the natural glue and also replaces it with whatever the tanning chemicals used after which the hides must be stretched until dry or the natural glues remaining make it hard again, btw that's why your veg tan gets harder after wetting it!!!  And that is where hide glue comes from, by slowly steeping raw hide in hot water!!! Then you add oils to soften the hides in the same manner as oil is used to remove gum from your kids hair, it breaks the bonds of the natural glues holding the fibers together.

 As for shrinking yes they shrink back to the original size some more than others depending on the stretching methods used. The hat brim i did the other day shrank about 1/4" all around  after i finished it the other day even after tooling it and i used no dyes. Dyes aren't the culprit its a matter of how much the hide remained over stretched during tanning.

[Matt S]

Leather can certainly change size or shape after different processes. I'm sure we've all had straps which suddenly get unstraight as soon as they get cut off the hide -- just from relieving some of the internal stresses. I've had straps where the stitching can stretch the leather (a curve develops if you stop having stitched just down one side Putting a piece through a machine like a splitter can stretch it too, as can even hand skiving an edge on certain leathers.

If any potential stretch/shrink/warp is likely to cause problems I tend to cut the initial pieces oversized and trim down once most of the work is complete. Linings can be trimmed to the edge of the "main" piece, or both pieces of leather deliberately cut slightly oversize and the outer edge of the entire lamination cut to final dimension. Yes it's a bit of a waste but I figure it's less wasteful than throwing out multiple large pieces cos they don't fit.