Silica gel is a very simple inorganic compound, but there are some
proprietary formulations with respect to the particle size etc.
'Premium' versions have a color indicator - - believe it is an organic
dye, but name escapes me at the moment - - which indicates degree of
saturation by color change. Reviewed several pdf files available on
the web last night. There is no fundamental reason the basic silica
gel can not be recycled ad infinitum. The organic dye indicator, as
would be expected from an organic, tends to degrade with repeated
heating cycles. While there may be some change in the physical
configuration of the granules, this does not appear to adversely impact
the effectiveness. I buy bulk material, pour it into a cotton sock so
thickness is about 2cm or less then knot the end - - and the toes if
holes present! Nothing glamorous here....... Most people feel
compelled to pour the gel granules into a pan then heat at circa 300°
in an oven to dry. Too much fussing for me. I have been placing the
filled sock on a plate in the microwave and heating for some arbitrary
time, circa 3-5 minutes. I then remove and rock up and down to provide
some circulation and let the moisture evaporate from the cotton sock.
If the sock remains damp, just repeat. (VERY scientific :^)), but
extremely effective and QUICK. Once dried, I store in a large glass
soup pot with a lid. When packing a camera bag in rainy weather or for
an extended trip, I just use the silica gel socks to pad lenses,
camera, etc. in my gear bag.
Was hesitant to mention the microwave drying earlier lest the slings
and arrows never end. This is kitchen science, not a procedure known
to be 'certified'. All bless the web. Found a pdf file on the web
from one of the large suppliers which gives all and infinitely more
that one would ever want to know about reclamation of silica gel. This
document verifies that microwave heating is effective albeit more
difficult to titrate. An old cotton sock, bulk silica gel and a
microwave - - - pragmatic, cheap and effective. The microwave drying
cycle is so quick and easy that even I can tolerate!!.
I'll send the other data later. It is in HTML and PDF and not sure if
it can be distributed on the newsletter. Can someone tell me if a
small PDF file will fly???
Hope this helps.
On Thursday, August 14, 2003, at 07:33 AM, Wayne Harridge wrote:
I was talking to a bloke tonight and he reckons silica gel can only be
dried out and reused a few times. Is there any basis to this - I
assumed it could be dried and reused indefinitely ?
Almost missed the last question: Heating to circa 115°F / 38°C is
essentially hot sunshine. This will not 'sterilize' the spores. Key
is that virtually all fungus spores just do not grow/propagate above
32-35°C. They STOP growing. Fungal spores are EVERYWHERE in our
environment, the air, water, etc. It would be hopeless to attempt
'sterilization' unless maintained at surgical room standards. The key
is understanding that the fungi just stop growing above ~35°C, a
temperature to which equipment can be stored without risk - - -
presumably. Fungus will grow at least down to freezing temperature.
We all know it will grow on food in the refrigerator. Elevated temp is
the simplest remedy at home and my personal opinion says silica gel is
practical for travel if you deal with it on a simple basis. Exchanged
several interesting notes with CH Ling last night. I misunderstood his
original post. He has a food desiccator appliance or box designed for
what I would expect to be used for drying fruit, etc. Very fancy, but
a bit expensive IMHO. An insulated box such as a hot/cold picnic chest
with a latch and tiny light bulb inside should accomplish all the
heating that is needed. A thermometer can be inserted through a hole
in the lid to monitor. This is a creative group....... All you really
need to know is lower the humidity or raise the temp and your Zuiko
lenses will be protected.
Regards,
Bill
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