underdrawing on linen embroidery 1608

["Karin von Lerber, Prevart GmbH" <karin.vonlerber@xxxxxxxxxx>]

I have a linen embroidery, dated 1608, which has badly aged (turned
brown)  because of being mounted on a very acidic wooden board. The
embroidery is mostly worked in undyed linen, outlines only, with very
few details in coloured linen (eyes, grapes etc.). The embroidery is
trimmed with a bobbin lace in linen and black silk, whereas the black
silk is extremely deteriorated.
One of the problems I am wrestling with, is the underdrawing of the
embroidery. It is dark grey and seems to be applied in fluid form (with
a plume?), as e.g. towards the tips of the leaves, the line narrows down
to almost nothing. I am considering a water based treatment to get rid
of some of the acidity (measured pH depending on area 4.4 to 5), but
this means, I would have to use a buffer, possibly Ammonium acetate. I
am wondering:
- what material could the underdrawing be done with? Does anybody know
of thechnological studies in this domain. Most sources I have available
mention chacoal, applied through paper. But is this evidence based, or
are we copying over and over one single source? What I have here,
definitely is *no* such charcoal drawing.
- if the underdrawing were ink, I assume it might withstand a short wet
treatment (probably on suction disk); but if it were e.g. lead? would
the buffer affect the metal?
- and: what are the possible dangers to the fragile black silk when
using ammonium acetate (pH 7) as a self-buffer? Would I have to
partially tread the middle with buffer and only afterwards, when most
acidity is rinced out (hopefully) wet clean the lace *without* buffer?
The difficulty of this procedure being the necessary soaking-stage,
where a wetting of the bobbin lace would have to be prohibited...

Any experience reports, references to technological publications and
ideas are welcome.
I do have a detail image with the underdrawing, which I will try to
attach, but I don't know, if it will be filtered out before being
circulated to all of you. On the image, some grey bleeding/stain is
visible. I have to try yet, if this is caused by the underdrawing. I am
not sure, as the stains are almost black on the reverse, whereas the
underdrawing barely shows on the reverse, and is rather dark grey than
black. The detail shows an area, which is very well preserved otherwise,
to give a better contrast for the underdrawing. Other parts of the panel
have turned brown completely.

Sincerely,

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: karin.vonlerber@xxxxxxxxxx
www.prevart.ch