This is straight from Don Post himself!
A LESSON IN LATEX
Latex is a protein derived from the sap of a tree and has a limited shelf life. Latex used for mask making can deteriorate faster than the "pure gum" form used for making latex gloves. The latex used in mask making (slip casting latex) contains a clay filler to increase viscosity and cause the latex to hold its shape. Manikin slip casting latex, for instance, contains even more clay filler and is completely rigid.
The filler in slip casting latex also makes for a more porous structure making it vulnerable to attack from skin oils and/or spores that may implant themselves in the latex and grow there. Latex, because it is a protein, can also be attacked by copper or brass. If a mask comes into contact with these metals, it will immediately show the effects. If someone touches a penny or a brass door knob and then handles a latex mask, they will leave a gray fingerprint on the mask.
We do not see these effects in other latex items such as cleaning gloves, surgical gloves and balloons.
Dip casting latex contains no fillers. They are not "slip" cast in a negative mold. They are dip cast on a positive mandrill. During the casting process these items also are bathed in a chlorine bath. The bathing chafes the latex which closes the porous surface of the latex keeping out oils and spores. This bathing makes the latex smooth to the touch.
To prevent early deterioration to latex masks, there are several precautions a collector can take:
> Keep your masks away from direct sunlight or artificial UV light such as florescent light.
Milk is a protein. This is why plastic milk cartons have a rough surface to deflect the UV light rays.
> Keep in a cool room. A hot garage during the summer will accelerate deterioration.
>Be cognizant or your heating system.
Is the heat in your home from a coal or oil burning source? The oils will affect your masks.
>DO NOT allow your masks to come into contact with metals.
Wipe your hands before touching masks. Better yet, wear white gloves to truly protect your masks from oils, etc.
>Perspiration and skin oils can cause serious damaged to your masks. If you intend keeping your mask for a long time, wash it after use. Wash the interior of your mask with bleach after use.
> Use ONLY UNSCENTED talcum powder on the interior of your mask.
> When storing your masks, keep them in a plastic bag in a dark place at room temperature.
Follow these useful tips and enjoy your masks for years to come!