The pure silk textile which are raw worked or white degummed or dyed with light colours can show some small faults due to dark places on the warp or weft yarns.

This problem has been deeply studied by the Stazione Sperimentale per la Seta and the Centro Tessile Serico in order to recognize the impurities and find a way to eliminate them.

A preliminary study on polluting substances has been made with optic and scanning electron microscopy, microanalysis and infrared spectroscopy coupled with microscopy and thermogravimetry.

The analytic results have displayed two types of impurities:

• 
  Pigment impurities, which are discontinuous, showing grey-black particles rich in iron, probably caused by the contact with oxidized iron surfaces and liquid rich in ferrous oxide (spinning water, condensate etc.);
• 
  Rubber impurities, which wind up one or more silk filaments with a brown-ocher colour, proteic or lipidic, probably caused by stained, rusty or dark-rusty cocoons..

For both types of impurities some simple methods of identification and possible industrial treatments for their removal have been studied, which can be both applied during finishing of crude and degummed silk.

The results of the research have been discussed during a meeting at Centro Tessile Serico on 24th June 2009.