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Subject: Waterlogged wood Drying wood

Waterlogged wood Drying wood

From: Jonathan M. Leader <leaderj>
Date: Thursday, December 5, 1996
Gee, two wood questions in a row.

Thanasis Vellos first:

>There is a waterlogged piece of wood from a shipwreck in the sea of
>Crete. The density of the wood is d=0, 39 gr/ml and the relative
>humidity is 166,55%. These numbers show that the wood is generally
>in good condition. This piece of wood is also identified as oak.

To which Quoc Khoi Tran, who is not on the distlist, responds:

>For this type of wood I would suggest controlled air-drying or very
>slow air-drying in a closed green-room. At the beginning of the
>drying process the relative humidity of the atmosphere should be
>high (90%). It will be decreased step by step to the value of 60%;
>the monitoring of the drying is based on the weight and dimensional
>changes of the object.

I would like to offer a cautionary statement to this suggestion.
Controlled drying can be effective, yet it should not be considered
as a primary treatment for this artifact.

Oak can be difficult to effectively treat due to its internal
structure (refer to Oddy, W.A.  Problems of the Conservation of
Waterlogged Wood, Report No.16, National Maritime Museum, Greenwich.
--or--just about any other discussion). And, while it is unclear as
to the exact meaning of the 166,55%  relative humidity statement, I
suspect that we are talking about Moisture Content. Am I right? *If*
we are talking about a moisture content of 166, then we are talking
about a Class III wood in a relatively good state of preservation.

Waterlogged woods can not redistribute internal moisture properly
during drying due to several factors. The most important being cell
surface tension in the remaining wood. Typically, moisture attacks
the secondary cell wall making the resistant strength and
flexibility of the wood moot. Under the circumstances presented
here, some osmotic collapse of the interior and possible surface
cracking/checking is likely to occur from Quoc Khoi Tran's
suggestion (see Hawley, L.F. Wood Liquid Relations, USDA Tech. Bull.
248 1937--an oldy but a goody; or look to Kollman, F.F.P. and Cote,
Jr., W.A. Principles of Wood Science and Technology, Springer
Verlag, NY). Whether these structural changes, with resultant
damage, are acceptable or not is up to the artifact "owner". My
personal opinion, for whatever it is worth, is that it is not
acceptable.  I would encourage a more normal treatment.

I am also concerned that no mention of the salt content acquired
from the "sea of Crete" (hygroscopic and prone to crystallization)
has been addressed.

Second, Xavier Hiron:

>We are dealing with a peculiar case of (waterlogged?) wood
>conservation. It is a wooden sculpture (Iron Age, 180 BC) found on
>an archaeological digging, which does not present the usual aspect
>of waterlogged wood. Its drying seems to be very advanced but it
>still has a water content (between 30 to 50 %). Its surface is
>attacked by micro-organisms as deep as 1 cm which makes it very
>powdery. We already did a gamma radiation to sterilize it but we can
>not immerse it into a bath for a classical PEG impregnation followed
>by freeze-drying.

Now this is really interesting. Would you please elaborate on the
site provenance/environment, tests done, surface details, and
facilities available.

Jonathan M. Leader. Ph.d.
1321 Pendleton Street
Columbia, SC 29208
Fax: 803-254-1338

                  Conservation DistList Instance 10:53
                Distributed: Thursday, December 5, 1996
                       Message Id: cdl-10-53-003
Received on Thursday, 5 December, 1996

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