Hi,
Some years ago there was a discussion of the use of PEG to preserve or stabilize
green, old, or ancient wood.  Several members pointed out that the use of PEG in
preservation of an ancient ship (Viking??) was proving to be a disaster in terms
of long term preservation.  Last night I read the National Geographic article
Robert Kunzig 2014. An ancient wreck tells the tale of Romans in France.
National Geographic. 225, 4. 120-135.
The following is a quote taken from page 134 if that article.
“Mud had protected the wood of Areles-Rhone 3 from microbial decay, but water
had dissolved the cellulose and filled the wood’s cells, leaving the whole boat
soft and spongy.  “The wood was held up only by water,” ...........  “if the
water were to evaporate, the whole thing would collapse.”  The solution was to
bathe the wood for months in polyethylene glycol, then freeze-dry it---gradually
infusing it with the polymer before removing the water.  But, the barge would
have to be cut in sections small enough to fit into the freeze-dryers.”

It seems that numerous sources and even my long ago college botany, wood
products/anatomy/pathology, and identification courses challenge the simplicity
of the above explanation for degradation.  However, what about the sketched out
method of preservation?? ?? Does the use of freeze drying in some way alter the
long term preservation value of PEG.  Alternatively, with both species and
environment influencing degradation is the wood in the Roman barge somehow
different from that of ships poorly preserved (in at least the long term) with
PEG.  A quick glance found more than several articles dealing with variation in
the state of ancient wood deterioration due to species and the environment it
rested waiting of us.

Perhaps, sadly, given the described extreme budget and time constraints, the
team did not have the freedom to decide on an optimal method for the long term.

Thanks in advance for any comments about the above.  I will be off line for at
least 10 days; hence, I look forward to reading any on or offline comments.

Cal Meier
Central Louisiana
Under the porch but benefiting greatly from what filters down.

Cal

This is still a developing technology.  The boat you are thinking of is the Vasa
now in its own museum in Stockholm.  Just google Vasa and images for an
unbelievable look at baroque ship building.  In 1961, they raised the ship after
350 years in the harbor in 120 feet of cold, brackish water and found a state of
preservation that is truly remarkable even on the parts that were not submerged.
They started spraying it with PEG shortly after and it took 20 years (IIRC) for
the PEG to fully displace the water and saturate into the wood fibers.

So twenty years after that, they discover that the PEG is “melting” the
structure of the wood cells - that is the word I was told best describes what is
happening as the wood structure is softened..  Now they have to figure out how
to get something else to displace the PEG.

Perhaps this freeze-drying technique is a way to alter the chemical composition
of the PEG?  Or to allow it more quickly displace the water in the cells with a
smaller amount?  I don’t know the answer to that.  I am staying with relatives
right now and they have the NG  - I will check out the article for sure.

Ed Minch





On Apr 6, 2014, at 4:02 PM, Cal Meier  wrote:

> Hi,
> Some years ago there was a discussion of the use of PEG to preserve or
stabilize green, old, or ancient wood.  Several members pointed out that the use
of PEG in preservation of an ancient ship (Viking??) was proving to be a
disaster in terms of long term preservation.  Last night I read the National
Geographic article Robert Kunzig 2014. An ancient wreck tells the tale of Romans
in France. National Geographic. 225, 4. 120-135.
> The following is a quote taken from page 134 if that article.
> “Mud had protected the wood of Areles-Rhone 3 from microbial decay, but water
had dissolved the cellulose and filled the wood’s cells, leaving the whole boat
soft and spongy. “The wood was held up only by water,” ...........  “if the
water were to evaporate, the whole thing would collapse.”  The solution was to
bathe the wood for months in polyethylene glycol, then freeze-dry it---gradually
infusing it with the polymer before removing the water.  But, the barge would
have to be cut in sections small enough to fit into the freeze-dryers.”
> 
> It seems that numerous sources and even my long ago college botany, wood
products/anatomy/pathology, and identification courses challenge the simplicity
of the above explanation for degradation.  However, what about the sketched out
method of preservation?? ?? Does the use of freeze drying in some way alter the
long term preservation value of PEG.  Alternatively, with both species and
environment influencing degradation is the wood in the Roman barge somehow
different from that of ships poorly preserved (in at least the long term) with
PEG.  A quick glance found more than several articles dealing with variation in
the state of ancient wood deterioration due to species and the environment it
rested waiting of us.
> 
> Perhaps, sadly, given the described extreme budget and time constraints, the
team did not have the freedom to decide on an optimal method for the long term.
> 
> Thanks in advance for any comments about the above.  I will be off line for at
least 10 days; hence, I look forward to reading any on or offline comments.
> 
> Cal Meier
> Central Louisiana
> Under the porch but benefiting greatly from what filters down.

PEG is still used for budgetary reasons, but it now has other chemicals mixed in
to reduce the potential damage.  The ship you mentioned that is a prime example
of the damage of PEG is not Viking, but it is Swedish:  it is the great ship
VASA.  Due to the interaction of PEG with other chemicals in the wood over time,
and the mobility that PEG gave to those chemicals, the VASA is now full of tons
(no typo) of sulphuric acid.

A better approach would  Have been to add bulk and stability to the cells by
means of active hydroxyl-ended polymers, same as the best practice for leather.

J

Joseph Sullivan