Smoke machines Haze machines

This is a response to both Paul Harrison's enquiry (Instance 16:13)
and Alayne Alvis's (Instance 16:14).

As has been pointed out, some "smoke" machines work by cooling the
air below dewpoint, using solid CO2 or liquid nitrogen, which
produces a cloud of water droplets.  This is unlikely to be harmful
to objects, as the low temperature/high relative humidity will only
be transient.

Other smoke machines work by producing a cloud of droplets of other
substances which do not evaporate, thus producing a longer-lasting
"smoke".  Some, if not all, Le Maitre machines use propylene glycol
as the smoke medium.  This is non-toxic and water soluble, and is
harmless to people, but it is sticky and hygroscopic.  It will
eventually deposit on surfaces where it will collect dust and water
vapour.

We had a hard job persuading a film company not to use one of these
machines in one of our properties which contains historic textiles.
They couldn't understand why we couldn't put the curtains through
the wash to remove any residues after the shoot.

One of these machines was also implicated in causing rusting of
unprotected iron fittings in a reconstructed 16th century gundeck,
where a smoke machine was used to simulate cannon smoke.

Barry Knight
Senior Conservation Scientist
English Heritage
London


                                  ***
                  Conservation DistList Instance 16:17
                Distributed: Tuesday, September 3, 2002
                       Message Id: cdl-16-17-006
                                  ***