Michael,

It sounds suspiciously like you have a Celluloid imitation of
tortoiseshell, particularly the geometric cracking and the powdering.

Unfortunately, once celluloid starts deteriorating, there is virtually
nothing you can do to completely arrest it. From your description, the
celluloid is in an advanced stage of deterioration, which has its own
difficulties. I just published a paper in Northeast Historical Archaeology
on Cellulose Nitrate (Celluloid) Plastic Identification and Care, with a
bent towards archaeologists encountering this material in the field. I'll
summarize some of the conservation concerns below:

- five stages of cellulose nitrate deterioration (initially for cellulose
nitrate films, but similar progression can be expected for more solid
objects, albeit at a slower rate): progressive yellowing (to dark brown),
checking and crizzling, formation of bubbles or foam on the surface,
embrittlement and shrinkage, powdering. All stages accompanied by foul odor
of nitrogen oxide gases. These visual changes are accompanied by a decrease
in auto-ignition temp. -- undegraded cellulose nitrate auto-ignites at
about 325F (150C); in the last stages, when all that is left is a powdery
or foamy mass, this temp. can drop to as low as 125F (50F) - easliy reached
near light bulbs, heat sources, and in unventilated storage areas in summer
months.

- light, heat and a high RH encourage deterioration of cell.nitrate;
degredation also accelerated by presence of acidity, alkalinity, or certain
metals which may be found as impurities in the plastic, or as component
parts of the object. UV light particularly harmful - breaks the cellulose
polymer backbone, weakening the plastic. Once begun, this will continue
even in the dark. Moisture, including RH, readily combines with nitrogen
gases produced during detrioration, forming harmful nitric acid.

- ** Ventilation and exclusion of light are most important factors in
maintaining stability **  Ventilation removes nitrogen oxide gases from the
vicinity of the objects. Pack loosely, to encourage air circulation (a
closed bag is a poor idea!); there should be at least one complete air
change per day. Oxygen-free storage of cell.nitrate is not recommended, as
this will accelerate deterioration. Cell.nitrate should not be exposed to
sunlight or illuminated strongly; consider it particularly vulnerable to
light, and expose to no more than 50 lux.

- RH: should be kept in an environment with an RH below 40%

- Temperature: Store below 68F (20C), with 50F (10C) preferable. Temps
should NEVER be allowed to rise above 85F (30C). When moving objects to and
from cold storage, acclimitize them slowly to prevent condensation of water
vapor and thermal stresses. If a refrigerator is to be used for cold
storage, be certain that a  high RH is not produced during the
refrigeration cycle, as is the case in some frost-free models.

- Do not use buffered papers or other alkaline materials to store
cell.nitrate; while alkalinity encourages the degradation of cell.nitrate,
deliquescent nitrate salts may also form on the object.

- Deterioration products produced by cell.nitrate can harm other objects --
isolate degrading cell.nitrate objects, storing in a ventilated and
fire-proof area.

I hope this long-winded reply has been of some assistance!

Megan Springate
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