Question answered! I applied Nair Sensitive to a piece of hand-dyed silk fabric through a stencil and left it on for periods of 15, 30, 45 and 60 minutes before washing it off with soap and water. Result is pale pink/brown marks. The effect is not unlike Decolourant Plus where the colour of the fabric is removed and then replaced with the colour in the product. Since the Nair Sensitive packet claims it contains “Sweet Almond Oil and Baby Oil”, I worried that I’d get greasy looking marks on the fabric but there are none discernible.
The active ingredient of these hair removal products is calcium thioglycolate. Glycolates are keratolytic agents that therefore soften the outer layers of the skin. Both skin and silk contain proteins but I suspect that the Nair acts more on keratin. Certainly even after an hour there was no evidence of weakening of the silk fibres on my test piece.
More pics on my blog.