Wool and silk are both protein fibers.

The biggest difference in their chemical composition is that silk
contains NO SULPHUR.

Wool contains the amino acid cystine. This amino acid has 2 sulphur
atoms, which form a disulphide bond. This is also why wool, and not
silk, is attractive to moths, who for some reason like this cystine
linkage.

Refer to Mechanical Properties and Structure of Alpha-Keratin Fibres:
Wool, Human Hair and Related Fibres by Max Feughelman, Univ. of New
South Wales Press, 1997.

Kim
(fresh from a Textiles Analysis course)

-----Original Message-----
From: Textile Conservators [mailto:[log in to unmask]] On Behalf
Of Shirley Ellis
Sent: Thursday, June 30, 2005 9:01 AM
To: [log in to unmask]
Subject: Re: silk velvet


I found your response very interesting because I was always under the
assumption that silk contained NO sulfur.  It forced me to look into
some of my texts, including the one you cited, Timar.  Gordon Cook's
Handbook of Textile Fibres states "it does not contain sulphur", pg 164,
as does Joseph's Introductory Textile Science, 6th ed., pg 44 "No
cystine or sulfur linkages are present to form the complex structures of
the keratin polypeptide chain. Early studies indicating the presence of
sulfur in silk may have been based on the analysis of samples that had
been treated with sulfurinc acid, which would have left sulfur residues
on the fibers."  In any case there does seem to be some inconsistency in
the literature.  I'd be curious to hear from others.  Does it or does it
not contain sulfur?

Shirley

Shirley Ellis
Sr. Textile Conservator
Royal Ontario Museum
100 Queen's Park
Toronto, ON  M5S 2C6
ph:  416 586-5878
fax:  416 586-8036

>>> [log in to unmask] 06/30/05 2:41 AM >>>
I am astonished silk would offgas sulfur. Where would the sulfur come
from? From dyeing or from sizeing? Or could it be, you might have mixed
that up with wool, where the polymers are interlinked with sulfur bonds?
The only amino acids containing sulfur are cystine, cysteine and
methionine, if I am not mistaken. Of these, only  thwo amino acids are
present in low concentrations in the amorphous regions of silk at an
amount of 0.2% (cystine) and 0.1%(methionine) (c.f. A. Timar: Chemical
principles of Textile Conservation, London 1998, p.43). Even with wool,
you would have to strongly illuminate so as to liberate hydrogen sulfide
from the molecular structure of wool (cf. Jean Tetrault "Airborne
Pollutants in Museums, Galleries and Archives...." CCI, Ottwa 2003,
p.11). I would be very interested to know, if these small amounts of
sulfur containing groups in silk have proved to cause degradation by
liberating sulfur containing volatiles in any reasearch/test situations
I might not be aware of. As far as MDF is concerned, I am not sure about
precise levels of various compounds in the US, but in general your
regulations are more strict than ours; therefore I dare making the
following statement: long times ago, MDF offgased considerable amounts
of formaldehyde and acetic acid. Nowadays - at least in Europe - this
offgasing is below detection limit, if the boards are left in a well
ventilated room for 2-4 weeks prior to use. Depending on risk evaluation
(humidity will warp acidfree board, water damage can be deleterious with
acidfree board, MDF might pose some risk if not properly sealed or if
the wrong type is used, PE-type boards pose considerable problems in the
context of fire....) MDF might be more or less appropriate than other
materials. So, as always, it depends on each single case.

Karin von Lerber

--
Karin von Lerber
Prevart GmbH
Oberseenerstr. 93
CH-8405 Winterthur
Tel. +41 (0)52-233 12 54
Fax. +41 (0)52-233 12 57
e-mail: [log in to unmask]
www.prevart.ch



Jane Hammond schrieb:

> Thank you for the suggestions.  I'm  sure the objects conservator is
> not planning to use a product that would be so detrimental - perhaps
I
> misunderstood, and I'll suggest an alternative.  As for silk
> off-gassing, I should have thought of that myself rather than being
so
> focused on being "historically accurate".  Your reminder is
well-taken
> and appreciated.
>
> Jane
>
> From this perspective, it should be a bit easier to find something
> suitable.
>
> Than
> On Jun 29, 2005, at 7:35 PM, Judith Andrewartha wrote:
>
>> hello Jane
>> By MDF I'm assuming you are talking about Medium Density
Fiberboard?
>> Are you aware that MDF off gasses both formaldehyde and acetic
acid,
>> both used as part of its production?
>>
>> In the sealed environment you have described this would be quite
>> detrimental to the objects. Also silk velvet off gasses sulphur
>> products; I would be using a synthetic velvet as it is inert and more

>> stable over time.
>>
>> regards
>>
>> Judith  Andrewartha
>> Textile Conservator
>> National Museum of Australia
>> GPO Box 1901
>> Canberra, ACT 2601
>> Australia
>>
>> phone   + 61 (0) 2  6208 5153
>> fax  + 61 (0) 2 6208 5167
>> email   [log in to unmask] <mailto:[log in to unmask]>
>>
>> >>> [log in to unmask] <mailto:[log in to unmask]> 30/06/2005
>> 8:58:15 am >>>
>> I am looking for a source of silk velvet (light-weight), suitable
for
>> use as a backing in an enclosed frame containing ivory/gilded
metal.
>> The velvet will be use to cover the backboard of a shadowbox frame
>> which houses three ovals of carved ivory set in gilded frames.
>> Because of extensive mold growth the original wood backboard will
be
>> replaced, mostly likely  by  MDF covered with ragboard, over which
>> new velvet will be placed.  The original velvet can not be
salvaged.
>>
>> Can anyone recommend fabric sources that will sell small quanties (
a
>> yard?) of silk velvet suitable for conservation use? The original
is
>> of a caramel color, so I am prepared to dye, if a white or ecru
>> velvet can be found.
>>
>> Thank you for your recommendations.
>>
>> Jane Hammond
>> Adjunct Textile Conservator
>> The Intermuseum Conservation Association
>> Cleveland, Ohio
>