You still stumble across it at times though, in some cases of garment dyeing for T-shirts sewn up overseas and imported blank. Stains appear at a glance to be associated with tarring, but it is rather difficult to believe tarring should ever be found in a garment-dyed cotton product. This kind of staining is so awfully persistent that removal is impossible even with organic solvents, surfactants, or through reduction bleaching.

I have always suspected that such staining may have something to do with minerals and calcium and iron were detected in multiple stains through fluorescent X-ray analysis. In all likelihood, desizing, scouring and bleaching were carried out using water with a high calcium and iron content.

Chemicals used in such treatments can suddenly become insoluble in the presence of calcium or iron, forming within the bath a sort of tar, resulting in staining by adhesion to the substrate. This is probably a case where calcium or iron, though present only in a small amount in the water, becomes enveloped by the sizing agent or surfactant used, thereby losing hydrophilicity and turning into highly inorganic dirt.

As a countermeasure against this kind of tarring trouble, the addition of a chelating/dispersing agent to the treatment bath will work well. For a trouble that may, or may not at all, occur, the employment of this additional agent in every garment-dyeing bath seems rather taxing, but it is something of a requisite, I would say, as a sort of insurance. This chelating/dispersing agent, which is probably based on the use of polymers of low molecular weight, seems to remove minerals by entangling them at the very moment that tarring is about to occur. Agents similar to Kao's product developed a while back have now taken hold, available from various manufacturers. This is where these agents may play an active role. (TT)