Arochlor

Posted on behalf of Monona Rossol <actsnyc<-at->cs<.>com>

    I don't know some of you are old enough to be working when
    Aroclor (PCBs) was still being used. But PCBs are really heating
    up as a subject with EPA's recent announcements about caulks.  I
    think it would be a good time to bring up management of historic
    slides mounted in Arochlor.

    People should know about the procedures that were used to make
    these glass microscope slides. The sample for viewing was placed
    in the middle. An optically clear liquid was added and another
    thin layer of glass was put on top. But if the item to be viewed
    was taken from a famous painting, a historic artifact, a rare
    plant or animal, or fossil, it would be kept permanently. In
    this case, the liquid in which the item was mounted was actually
    a syrupy thick Arochlor. The slide was heated to reduce the
    Arochlor's viscosity and remove any bubbles around the item.
    When the thin slide cover was placed over the liquid, it cooled
    and hardened producing a permanent slide with excellent optic
    properties that would last essentially forever.

    It was common for excess Arochlor to squeeze out over the edges
    of the slide and cover. Many labs had a small wet grit grinder
    for taking off the hardened excess. And that wet grit full of
    PCBs dried in between uses creating a contaminated dust. This
    dust usually was just dumped in the trash as ordinary waste.

    Museums used Arochlor well after EPA banned manufacture of PCBs
    in 1979. I remember that they got this exemption on the basis
    that there was no substitute. The only other substance that was
    used similarly was balsam resin which is not as good. Museums
    eventually stopped doing this. But now those slides, each with a
    drop or two of pure Arochlor on them, are not something they can
    dispose of easily because they are historic research and
    teaching materials.

    My questions for you are:

        Do you know when museums stopped using Arochlor? I know I
        still found the stuff in labs in the 1990s, but often the
        conservators claimed it had just been there a long time and
        they didn't really know what it was for.

        Are museums keeping or disposing of these historic slide
        collections?

        If they keep the slides, are there any precautions they are
        taking to prevent exposure to the users, notification of
        fire authorities in case the collection were involved, etc.

        What are they making permanent slides with now?


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                  Conservation DistList Instance 23:15
                 Distributed: Friday, October 30, 2009
                       Message Id: cdl-23-15-015
                                  ***