TARA

GENERALITIES

It is a small thornbush tree with reddish flat pods which grows in the dry areas of Peru, South America.

Caesalpinia Spinosa

For tanning purposes, only pods are of some interest. They can be selected, ground and sometimes sieved depending on the way of working and the reliability of the company which collected them.

HISTORY

Tara pods, mixed with iron, were used by Pre-Colombian civilisation 3,000 years ago as a black dye.
The high content of hydrolysable tan had made it very interesting for the extraction of gallic acid and ink manufacturing.
For tanning purposes, although used by autochtone people for centuries, its applications at an industrial scale are in fact relatively recent.

COMPOSITION

Tara belongs to the pyrogallic family and more exactly to Caesalpinia Spinosa group.

Raw material has a tan content between 35 and 55 % and after extraction this percentage can rise to 72/75 %.
Impurities contained in Tara are iron, free gallic acid and unground thorns.

PROPERTIES

What makes the difference between Tara and the other vegetable extracts is that, used alone on pelt, it gives an off-white lightfast leather. This is of great importance for the tanner who wants to dye in pastel shade with a vegetable caracter.
The lightfastness of Tara can be explained by the relative difficulties to oxidise the tans due to the slight content of free gallic acid.
Tara is also the extract for which the ratio tan/non tan is the higher along with a strong natural acidity. This is why Tara is basically the most astringent tan in the market. If this property is interesting when producing shrunken grain or hard grain leather, it could be a disadvantage if it is not used carefully.
When using Tara, great attention should be taken for pH control of both skin and bath which must be from 4.0 to 4.8. A way to avoid this problem is to choose the ground form of Tara rather than the extract. Fine ground Tara must have an average particle size of 200 microns, free of iron salt and thorns, with less than 20 % insolubles.
Consequently, before going ahead with Tara, the tanner should select the origin of the tan and exclude untreated raw material - although less expensive - to avoid great desillusion such as black spots, scars, bold grain during leather processing.
Refined ground Tara is less astringent than Tara extract allowing a versatile use in tanning and retanning bath. It can be an alternative to more common extracts and syntans because leather remains off-white and lightfast with a full hand thanks to the insolubles.
The gallic acidity of ground Tara (pH 3.2 / 3.3) makes it very interesting to fix the dye and other vegetable extracts of the catechol family (Mimosa, Quebracho, Gambier ...) and reduce the quantity of formic acid.
Another particularity of ground Tara is that because of insolubles it has an unknotted effect on pelt during tannage which is of great importance for some leathers such as reptile and crocodile ones.

COMMERCIAL BRANDS

RETAN TB
Ground and micronized Tara. Special care has been taken to minimize iron content. It is a versatile product and perfect alternative of synthetic tanning agent when retanning soft leather such as automotive one. Although just ground, this product contains more than 50 % tan and only 10-15 % insolubles.

RETAN TA
Spraydried extract of Tara pods. It contains 73-75 % of tan with high astringency. It is used only for special leather such as shrunken-grain, book-binding and crocodile.

RETAN TL
Liquid form of Tara. Very useful for automated tanning system. It is the whitest Tara compound.