Generally, the best mixed tannages for solid leather consist of a combination of both pyrogallol and catechol tannins.
The pyrogallol tannins give a bluish-black colour, and the catechol tannins a greenish-black, with iron salts.
Catechu tannin= and =catechin= are compounds of thecatechol tannin type.
These differ in their characteristic reactions as follows: Pyrogallol variety Catechol variety Ferric salts Dark blue Greenish black Bromine water No precipitate Yellow or brown precipitate Leather Produce a "bloom" No "bloom" Conc.
Like all catechol tans, the resulting leather darkens on exposure to sunlight.
They naturally influence the colour of leather made with catechol tans, which is usually distinctly redder than the leather made from pyrogallol tans.
They are all, however, derived from either catecholor pyrogallol, and yield these substances if carefully heated to about 200 deg.
Mallet bark yields another catechol tan similar to that of mimosa, but somewhat less astringent and more yellow in colour.
They are considered to be anhydrides of the catechol tans.
Mimosa bark is one of the most important catechol tans.
They make good morocco leathers for many purposes, but the primary catechol tannage renders them ineligible for finishing under the specifications of the Committee of the Society of Arts.
The phlobaphenes or "reds" are also typical of catecholtans from which grow catechins; they can be formed by boiling with dilute mineral acids.
Of these the catechins are the most typical, and have been considered as the parent substances of the catechol tans.
These skins are tanned with turwar bark, which contains a catechol tannin.
The tannins are classified into "pyrogallol tans" and "catechol tans," according to the parent phenol.
It is particularly advantageous to blend judiciously the two main types of material, the pyrogallol and catechol tans.
In the list of materials two have been placed in a subsidiary class because they are a mixture of catechol and pyrogallol tannin.
Pyrogallol tannins include some of the lightest coloured and best materials known, and, speaking generally, the leather produced by them is not so harsh or hard as that produced with catechol tannins.
Pyrogallol tannins give a blue-black coloration or precipitate with ferric salts, and catechol tannins a green-black; and whereas bromine water gives a precipitate with catechol tannins, it does not with pyrogallol tannins.
The other is called the catechol group and is strongly condemned.
Among the materials belonging to the catechol group are hemlock bark and larch, used chiefly in this country, and turwar bark used largely in tanning East Indian goat and sheep skins.
On the other hand, leathers which showed the red decay were in every case found either to have been tanned with tanning materials of the catechol series, or were rotted with acid.
The large proportion of so-called moroccos offered to-day are made from skins tanned in East India with a catechol tannin.
Xanthin and catecholbrowns are pleasing in appearance, but their effect is less rich than that obtained with potash.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "catechol" in a variety of sentences. We hope that you will now be able to make sentences using this word.
