bleaching printed cotton

[Jenny Barnett <andelos@xxxxxxxxx>]

Dear colleagues,
Here is question concerning the possible bleaching of a Japanese print
on a cotton textile, probably early 20th C.. The textile is badly
stained brown by close contact with a strawboard backing in a glazed
frame. It has been washed but this was not effective. The staining is
also uneven and blotchy. In this state, it is not worth reframing it, so
the owner has agreed to a bleaching treatment. We are willing to take
the risk!

Having limited bleaching experience, I consulted quite a lot of
literature and came to the conclusion that bleaching with sodium
perborate as described in Timar-Balazsy & Eastop's "Chemical Principles
in Textile Conservation", page 231, would seem to be the best method.
This is because some of the printing inks may contain metal and a slow
process would be desirable to moniter the process.

This is how the method is described in the book:
"As a bleaching agent, sodium perborate decomposes to hydrogen peroxide
with a low reaction rate in the absence of catalysts.
A 10 g/l solution of sodium perborate buffered with a solution of boric
acid/borax buffer to pH 7 can be effective for bleaching.

I checked this out with a paper scientist and he found the pH 7
strangely low, pehaps even too low to be effective. Also, we could not
work out what the correct amounts of boric acid/borax should be in such
a solution.

The questions are:
Does anyone have experience bleaching Japanese printed textiles?
What are the correct amounts of boric acid and borax for this buffer
solution recipe?
Are there metals in black, blue, violet and light brown Japanese
printing inks?
Or is my concern about metal in the inks unnecessary?
Have I misunderstood anything?

I will certainly report back on the results of this query and the
eventual bleaching treatment.

All suggestions will be gratefully received,

Jenny Barnett
Andelos Textielrestauratie
Oude Looiersstraat 65-67
1016 VH Amsterdam
NETHERLANDS
tel/fax 00 31 (0)20 427 18 27
andelos@xxxxxxxxx