Rubber: Dry Rot, White Bloom (causes + effects)....
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David H65 wrote:
I have two Sigma camera lenses that has the same issue of stickie rubber surfaces.
Has anyone found a solution. The last post was in 2017.
All my cameras are kept in a cupboard in our house with air conditioning set at a constant 73 deg F.
I had a similar issue on the grip of a golf putter. I tried washing the grip, scrapping the grip.
Nothing worked. I do not want to take such drastic action with my lenses.
I replaced the grip with a new one.
Gummy rubber can be caused by several factors. Let me just share a few things that might help others figure out what is happening.
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BLOOM (white 'powder' on rubber)
On my own new Canon Mk III Extenders which are less than 2 years old and have been stored in dry sealed containers with no humidity, the inner rubber rims of the forward facing elements turned WHITE. This came away with the slightest contact with a soft cleaning cloth. The white is called "Bloom" and Bloom occurs when extremely high quality rubber is used. It's not mold. It's a component called a "stabilizer" that is deliberately engineered into the rubber to prevent Dry Rot. And Dry Rot is usually triggered by UV Light and tends to make rubber brittle. Seeing Bloom on your rubber is not a concern as it will come away with gentle rubbing. Cleaning it off doesn't defrade the effects of the protection and it may return when the objects are stored again. Seeing it rise to the surface is evidence that the compound is doing what it is supposed to do.
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Be wary of Solvents and Sunscreen
Tacky rubber surfaces are a very different matter. They can be caused by UV light breaking down the rubber and causing it to degrade. Either it will become sticky or it will become brittle. Sunscreen contains components that can degrade rubber and plastics and even insect repellent can do the same and may even turn rubber white from the chemical reaction (this is not Bloom). Be VERY wary of using sunscreen because if it ends up on your lens it can very often etch the vapor-deposited coatings from the lens elements. Use a UV filter if you need to work with sunscreen. Sunscreen is abrasive because it contains titanium oxide particles which cut away the coatings on the lenses and it also contains a penetrative oil that can get beneath the layers on the glass and help lift them. Using alcohol will remove the outer layer that has started to become unstable but it's very likely the stickiness will later return. Talcum poweder has sometimes been recommended but that only acts like baking powder on pudding. Eventually the moisture will seep through and then you'll have talc in the sticky material. Rubbing with alcohol should be done carefully to avoid getting it into the seals of the lens. And you will get quite a bit of residue on the rubbing cloth that you use... it will probably become black as you rub away the sticky surface but it ought to work for the short term.
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Another cause of tacky rubber is solvents. There are chemicals in perfumes and oils that can penetrate rubber and cause it to become tacky. As rubber (and this includes latex) gets older it becomes sticky as the rubber degrades. I think that one way to resolve this might be to gently wipe the sticky areas with pure alcohol. 70% alcohol will also work. Some have said that WD-40 will work as well but you MUST be very cautious with such things because WD-40 contains penetrative oils that will find their way into the lens though any cracks.
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Dry Rot
Dry rot is an expression used for all different materials but when used in reference to rubber it's not about real, actual Rot but simply the rubber becoming brittle. it has nothing to do with fungus. On the other hand, Dry Rot in Timber is usually fungus related. Ultraviolet radiation, Temperature Fluctuation and Oxidization are all causes of Dry Rot in Rubber. It occurs when time allows the stabilizing compounds in the rubber to rise to the surface. Time itself is an influencing factor. These causes then allows the rubber's molecular chain to break down as time progresses, causing it to become brittle. The breakdown allegedly begins to occur the moment the rubber is first molded into shape at the manufacturing plant. Sunlight is probably the biggest cause of Dry Rot in rubber although most glass window panes actually block most of the UV light (which is why you can't get much of a tan sitting in front of your window in the middle of winter).
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Camera Gear rubber products
Refined rubber sap is latex. When rubber is cured for use in camera gear, it is heated with sulfur in a process called Vulcanization. This causes the polymer chains in the latex to link together in a network. This results in a product that can be flexed and even stretched but it is no longer sticky. When the environment causes rubber to become unstable, it will either dry out and crack (Dry Rot) or it will begin to revert back to its original state (Sticky!). The mesh of polymer particles starts to snap and the rubber reverts back to smaller chains... which is why the rubber starts to get sticky as it returns to its latex origins.
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Two Solutions: Replace Affected Part or Replace Product
The bad news here is that once rubber starts to destabilize, it will either become brittle (dry rot) or sticky (molecular dehesion). There's no way to reverse the process and using alcohol is more or less a temporary solution to the problem. It may work for long periods of time in some instances although you should check the rubber under magnification to ensure it's not splitting or crumbling anywhere at the same time. I'm afraid that only the manufacturer can replace the rubber. If they cannot or it's too old or expensive to replace, the only solution is to dispose of the lens and buy a different one.
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It's actually quite sad to deal with these things... because you can take good care of your products and still have this happen. And adding dry-satchels to dehydrate a container with your lens in it may stave off dreaded lens mold but it may contribute to dehydration and degradation of the rubber itself.
