Heating museum materials

Nynne Sethia <nynnecarl [at] hotmail__com> writes

>I'm working for a museum of cultural history, which is in the
>process of establishing a treatment facility against pests. The
>museum can afford to get a room which can either freeze or heat the
>objects. As a conservator I initially opposed the idea of heating
>museum objects, but it seems to have a few, but very important,
>benefits: If saves a lot of time, because you don't have to wrap
>each object carefully and tight, and it kills both insects and
>mold/fungus at the same time. ...
>...
>... Is there anyone using or
>experimenting with heat treatment, who can give me some comments on
>their experience? If so, which material don't you heat (48 degrees C
>is said to be the minimum for killing insects)?

After years of freezing keratins in chest freezers and occasionally
the freeze-fryer, we tried heat treatment a few years ago and now do
a project every summer.  It seems ideal for flat textiles like rugs
and blankets where it is questionable that you are getting the
desired low temperature right through the object in a chest freezer
which always seems to be full.

What we do (this is based on conversation with Tom Strang at
Canadian Conservation Institute) is use a sunny cement courtyard
where sun is captured and bounces off surrounding concrete block
buildings.  Then:

    *   We lay down several sheets of 2 inch Styrofoam SM, covered
        by a vapour barrier of 4ml polyethylene sheeting.

    *   we lay out the vacuumed, condition reported mats, rugs,
        shawls etc on this up to 2-3 layers deep, inserting the end
        of a digital temperature probe (ca $15 at radio shack) at
        3-4 points around the layout

    *   we cover the works with a *black* polypropylene tarp,
        tucking the ends under and weighting the edges with 2 x 4
        inch boards

Usually on a sunny July day in Newfoundland, the temperature will
reach 50-60 deg. C in about half an hour.  Most other places it will
get much hotter, much faster that time of year.  Since 48 deg. C is
adequate, you certainly don't want to go any higher than 60 deg. C
because there's no benefit to justify the risk.  We monitor the
probes and leave them for at least an hour.

We then re-roll them and tag them re treatment/date.  We usually
store treated keratins in zip-lok bags or heat-seal them in 4 ml
plastic  to prevent re-infestation, or confine infestation if
treatment for some reason is unsuccessful.  We also can assume that
if a keratin slips the net untreated into storage we can identify it
as untreated by the fact that it is not tagged treated or bagged.

We have so far had no activity in items treated this way but it's
only been a few years.  Certainly though this method has many
advantages over freezing for this type of material

    *   little concern re dimensional response since most of these
        objects are not under restraint in any significant way

    *   cheap, simple, fast

    *   can be sure you are getting effective temperatures

Smaller items we continue to freeze in the chest freezers in the
lab.  A walk-in freezer is planned for a new museum to be built by
2004; with that facility to routine freezing at point of intake
will become more practical. but I doubt we'll ever abandon the
"backyard" method for flat textiles.

Rose Smart
Newfoundland Museum
St.John's, Newfoundland, Canada


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                  Conservation DistList Instance 15:59
               Distributed: Wednesday, February 27, 2002
                       Message Id: cdl-15-59-004
                                  ***