Re: Ultrasonic cleaners...

[Constance <cnstnce@xxxxxxxxxx>]

This is one of the many areas that is still worthy of further study.
Can ultrasound be adapted for any application in textile conservation?
For instance, could megasonic cleaning have some usefulness for
archaeological textiles?

This particular device, The Buzz, proved useful here in helping to
break up and disperse hard, oxidized grease deposits on a Central Asian
looped pile mat.   These deposits did not yield to surfactant solutions
nor a variety of solvents at acceptable pH's and temperatures - even
with prolonged treatment.  Enzymes could have been effective, but I
wanted to try the device  The cleaning liquid that is supplied with the
machine has the polar solvent dipropylene glycol monobutyl ether as the
active ingredient - about 1-4%.  There are three power settings.  In
practice, I used my own solutions.  I was unable to monitor changes in
the condition, since the fibers were completely encrusted by the
solidified, rock-hard grease prior to treatment.  Microscopic
examination after treatment showed no fibrillation.  It should be used
always with a soft padding under the area being treated i.e. do not use
it on a textile laid against a hard surface.

The dental ultrasonic descaler has proven particularly useful in
helping to remove ink signatures on Indonesian textiles - in
conjunction with a vacuum table.  The work is monitored at 60x and
damage is not observed when used carefully.

The ultrasonic descaler is very aggressive when used on hard surfaces.
Ultrasonic waves are reflected from hard surfaces as "rarefactions" and
result in solution cavitation near that surface.  The cavitation is, of
course, extremely damaging.  Near soft surfaces such as textiles, the
waves are reflected as compressions - and cavitation is inhibited by
impedance.  The role of ultrasound in textile cleaning is then is to
accelerate the action of surfactants and solvents.  This is the theory.

The application of ultrasound in the bath is different from the use of
these two tools.  Study of ultrasound for textile cleaning (a master's
thesis that is begging to happen) would include type, size and
distribution of transducers; solution chemistry; support of textiles in
the bath;  providing a means of moving the textile in the bath through
the standing waves for even cleaning; tuning of power and frequency to
maximize cleaning and minimize damage in response to the temperature,
chemistry and geometry of the bath.  Physical and chemical properties
of fibers would have to be monitored.  A daunting task.  This is why
little has been done since Goldwasser's patents of the early fifties.
More recently, Gary Mock et al. have done some studies on ultrasonic
effects in textile wet processing.  Through the years there have been
several papers discussing damage to feathers cleaned by ultrasound.

Even with cavitation controlled, the primary problem of ultrasound may
prove to be the formation of radicals that are reactive with dyes and
fibers.

David Walker

Talisman Restoration, Inc.