Posted: 24 January 2010 at 12:58pm | IP Logged

Acid black 210 is sensitive to chromium salts and, for this, is not advisable its use as a charge changer for top dyeing using stuffs like Luganil Black NT.

Posted: 26 January 2010 at 8:27pm | IP Logged

Chrome complexes with the dyestuff changing the hue by "metallization" and the brownish-red black becomes greenish (or viceversa!). 

Posted: 31 January 2010 at 11:49am | IP Logged

EDTA sodium salts have available anionic carboxyl groups that "mask" collagen's charged aminos and perhaps even bridge across them, thus potential surface "bleaching" results, affecting the dyeability of collagen by anionic dyes as well as causing an additional weak tanning effect as well.  If the dye solution itself is treated with such EDTA products in the absence of collagen, most likely what Mexgerber reports occurring is very true, but adding such EDTA derivatives to collagen at acid pH values causes a reaction with the protein's charged amino-side groups that blocks posterior dye fixation and imparts softness upon drying by blocking charged aminogroups from forming longer distanced saline bonds, much as a aromatic sulphonic bearing syntans do, with similar muted and leveled dyeing properties results.

The reason I suspect this happens is that by adding such EDTA products in the basification step of wet-blue, causes a lighter color (EDTA chrome complexes are less blue-green than sulfate-formate ones) than the usual but results in no obvious diminution of boil-proofness in the leather itself, hence stripping off of chrome as oxalate will definitelly do, is not the case!