Re: bleaching printed cotton

[Season_Tse@xxxxxxxxx]

Helen Burgess' bleaching review mentioned dithionite.  Sodium dithionite is a
less powerful reducing agent compared to sodium borohydride, but it does have
the unique ability to reduce iron containing stains, and it does work at a
neutral pH.  I would imagine if the stain is somehow caused by the presence of
iron, then dithionite will work while borohydride will not.  But foxing stains
are very difficult to remove with reducing agents, I have never seen it work,
but oxidizing bleaches, including light bleaching, seemed to have more success
in reducing fox spots.  And I totally agree with Vivien's comment about thorough
rinsing.

Season

Season Tse
Conservation Scientist/Chemist
Conservation Processes and Materials Research
Canadian Conservation Institute
Dept. of Canadian Heritage
1030 Innes Rd.
Ottawa, Ontario
K1A 0M5
Tel. (613) 998-3721 (x-187)
Fax. (613) 998-4721
email:    season_tse@xxxxxxxxx

Visit the CCI Web site at http://www.cci-icc.gc.ca/




Textiles & Organics Conservation <tex-org@xxxxxxxxxxxxxxxxxxx> on 02/20/2002
10:28:08 AM

Please respond to texcons@xxxxxxxxxxxx

To:   texcons@xxxxxxxxxxxx
cc:    (bcc: Season Tse/HullOttawa/PCH/CA)
Subject:  Re: bleaching printed cotton



Dear Jenny, and other colleagues,

>From time to time and in response to pressure to do "something" I have
had some success with sodium dithionite (hydrosulphite), a reducing
bleach, also sold (supplied as samples?) by BASF compounded with buffers
as Blankit 1N. You can use it locally by moistening the stain and
applying the powder. Ventilation/fume cupboard advised, and I'd want it
to be the sort of object I wasn't afraid to rinse thoroughly. Used as a
dye stripper industrially, but has worked on indeterminate brown stains.
Can anyone point me to any scientific evaluation of this?

Vivien Chapman
Head of Organics Conservation
Conservation Centre, NMGM
Liverpool, England

n message <3C71FD14.339E4ACA@xxxxxxxxx>, Jenny Barnett
<andelos@xxxxxxxxx> writes
>Dear Season,
>Thank you for your extensive advice.
>I had already read the literature you suggested and have had some
>experience with sodium borohydride which was the stimulus to explore
>other solutions.
>That particular case concerned a small piece of 20th C. embroidered
>cotton with so-called foxing spots. It was a test piece so it was
>possible to cut it in half to see the difference before and after
>bleaching. The embroidery threads lost a little colour intensity as did
>the "foxing" and the cotton was significantly lighter. The result was
>more intense "foxing", so my conclusion was that the colour of the
>foxing was preserved just as well as the colours of the embroidery
>threads.
>I shall test the possible results with local bleaching with peroxide and
>with sodium borohydride to see which is most effective and suitable.
>Thanks for the reminder!
>
>Will keep you informed,
>
>best wishes,
>Jenny Barnett
>
>Andelos Textielrestauratie
>Oude Looiersstraat 65-67
>1016 VH Amsterdam
>NETHERLANDS
>tel/fax 00 31 (0)20 427 18 27
>andelos@xxxxxxxxx
>
>
>
>
>

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Textiles & Organics Conservation