Mural on steel bulkhead of battleship

Susan Smyer <Susan.Smyer [at] tpwd__state__tx__us> writes

>We have a mural painted on a steel bulkhead/wall in a room that is
>being restored. ...
>...
>The mural itself seems to be of a stable oil-based enamel with no
>flaking.  ...
>...
>Do I need to do more to protect this mural after it is completely
>uncovered than cover it with a sheet of plexiglass with UV
>protection that is on spacers and provides air flow?

The idea of creating a shallow "display case" of acrylic or some
other material is sensible, but it is easier said than done. Even a
small temperature differential between the covered steel wall and
the room air could cause some dramatic effects on humidity level and
passive ventilation, and the polluted ambient air could also
complicate matters.

Purely passive ventilation could be very difficult to control.
Engineering correctly sized and placed holes would be a challenge.
Dust and dirt entering through the holes (filters would be too
restrictive on natural air flows) could also present quite a
problem.

Sealing the air beneath the glazing and using a passive system to
deal with humidity changes (eg silica gel) might also be
challenging, as the air space above the painting would be
particularly small relative to the other dimensions. Stratification
and lack of adequate air circulation might make passive humidity
control very difficult.

I would suggest using some kind of active microclimate system. Here
are some examples:

An active solution may be as simple as a case ventilation system.
These consist of a small and quiet fan and a set of filters to
provide constant positive pressure ventilation (air will be filtered
for dust with optional filters for gaseous pollutants). This system
will not provide humidity control, but may provide enough
circulation to maintain adequate humidity levels if the room is
fully climate controlled. A cheap and cheerful solution.

A hybrid device (a passive reservoir and a fan controlled by an
electronic sensor) will provide limited air circulation, and take up
less space than a similar amount of silica gel. The advantages of a
hybrid system are independent control of the air space below the
glazing, and the extremely long times between maintenance for the
media. A little more expensive than case ventilation with ambient
air, but far more controlled. These devices are a good option when
humidity control is consistently "one way" (eg always
dehumidifying).

More complete control can be effected by using a full microclimate
generator to provide temperature sensitive humidity control. There
are a variety of systems now available; all use fans or pumps to
provide a constant flow of humidity adjusted air controlled by an
electronic sensor in the display area. These devices can be combined
with various filters, and can be located at some distance from the
enclosures to be treated. Not necessarily "cost effective" if only
one small enclosure is to be treated, although dramatically less
expensive than silica gel when larger volumes are involved. A
sophisticated solution, but do you know of any really cheap
sophisticates?

All active solutions may be elegantly built in to your glazing
system if you plan ahead.

More information on microclimate control devices may be found on our
new site at: <URL:http://www.keepsafe.ca/MTI>

Jerry Shiner
Keepsafe Systems
Supplies and Solutions for oxygen-free and microclimate storage by
Mitsubishi Gas Chemical  America and
Microclimate Technologies International Inc
800-683-4696


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                  Conservation DistList Instance 17:28
               Distributed: Wednesday, September 10, 2003
                       Message Id: cdl-17-28-004
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