Clark - Dying leather and dying cloth are generally two completely different things (in fact even dying cloth is different dependent on the dye) and comparing the two directly can be frstrating at best. For instance in general leather does not need a mordant since tannin is itself a mordant. On the other hand there are differences in tannins:
The Two Types
There are two types of tannin: Catechol and Pyrogallol.. By understanding when to blend these together, the expert tanner could reputedly create the appropriate leather for any need: hard and firm, mellow and soft, light or heavy. Until you are an expert and can even notice the differences, I wouldn't worry about it, but it is interesting to pay attention to as you tan.
Catechols (aka condensed) are more astringent and tan more quickly than the pyrogallols. They deposit a reddish sediment known as 'reds' or phlobaphenes. They make leathers of pink, red or dark brown hues, that are more 'solid'. They also create greenish-black spots on contact with iron. Mimosa, birch, hemlock, quebracho, alder and fir bark contain catechols. Oak bark contains both types.
Pyrogallols (aka hydrolysable) deposit a pale-colored sediment called 'bloom' (elegiac acid} which, if deposited in the leather, improves its solidarity, wearing properties and resistance to water. Hence they are favored for sole leather. They are also preferable for leathers intended for bookbinding, upholstery and other purposes where longevity is essential. The resultant leather is of pale color varying from creamy or yellowish to light brown. Pyrogallols make bluish-black spots on contact with iron and resist changes in pH value. Sumac, chestnut, oak galls and oak-wood contain pyrogallols.
source:
http://braintan.com/barktan/2tannins.htmThe following article discusses the problems dying black using hemlock tanned leather versus oak tanned leather - this appears to be due to the differences in the tannins noted above and may shed some light on why import hides at times have problems when using vinegar black. On the other hand I've never had any real problems getting a decent to good black even with import hides and have never had the problems that Stophel noted......
http://www.jarnaginco.com/cmharticle.pdfAs for logwood and leather - yes it is generally good for browns as is, for black it takes a bit more - just one recipe from the past I have is:
"Boil a quantity of logwood bark in double it's bulk of rain water (i.e. water that hasn't been tainted with minerals) for two or three hours, then strain off. Add 1/4 pound of potash to 2 gallons of the logwood liquor."
Note teh use of potash - a base like baking soda. In fact baking soda alone (or other stronger bases such as washing soda or potash) will darken leather, but I find that used alone they tends to "burn" the leather too easily when not carefully applied and that can be just a matter of seconds.
Normally tanned leather is rather stiff and hard. To make leather soft and supple they used to run it through a process known as "stuffing". The hides were thrown into a revolving drum. A non-oxidizable oil was added to the hides. The oil then worked its way into the hides as they tumbled. The oil makes the hides pliable. Acting as an "internal lubricant" in the porous structure of the leather. This also acts to waterproof the hides when they are made up into finished goods.
Thanks for your info Bill and it's still called stuffing. There are in fact two methods generally used, hot stuffing and regular stuffing aka fat liquoring. In period some of the most common oils used were: fish oil, neats foot oil, and tallow - beef and sheep mostly, although hog lard (aka pig tallow) was also used.
re: neats foot oil - originally rendered from the shin bones of neats aka cattle. Since the 1930's though neats foot oil made in the USA can be made from other sources (mostly hog lard these days per one of the major the manufacturers) as long as it's meets a certain Mil-Spec standard.
The "problem" with all oils in leather though is over time they either get "pushed out" to the surface due to water, sweat, and other factors so the leather drys out and gets damaged. In fact most dyes, especially modern ones that so often use thinners such as alcohol, toluene, etc. dry out, stiffen, and crack after application and why re-oiling/condtioning is necessary.
these links have some info of interest as well:
http://www.jarnaginco.com/leather%20definitions%20index.htmhttp://www.hermannoakleather.com/
