I'll be away this weekend, scuba diving on a sunken city in a reservoir somewhere in Zhejiang province. If all goes well --which is to say the fiddly and temperamental equipment performs as advertised-- I'll be shooting some underwater video in the reservoir. Anything good will be shared on this site. So will anything bad most likely, so don't get too excited. I've done a fair amount of underwater photography over the years, so hopefully things will come together.

I'm a tropical diver and unaccustomed to cold water. But the reservoir is cold. Hence, I've been learning to dive in a dry suit, and I spent much of last Sunday in the tank at the Blue Zoo working out my new suit (actually the suit loaned to me by Asian Diver magazine, for whom I will write an article) and enjoying the gasping wonder of the nongmin tourists in the acrylic tube. Some video of that has already been shot, so we're well on our way to a mini-documentary.

Aside from freezing my ass off, the other potential problem with cold water is fogging. Humidity in the surface air gets trapped in your mask and in the camera housing that you seal topside. In cold water the inside surfaces cool, and everything fogs over. With a mask you can rinse the inside of the glass with a little mild detergent such as Johnson's Baby Shampoo --no more tears!-- which will keep it clear. In sea water, cheapskates like me use spit, but that doesn't work in fresh water. If the mask fogs anyway, which it sometimes does, you can always rinse it out underwater and then blow it clear again (a basic scuba drill). You can't, however, do that with your underwater camera housing. Or you could, but you wouldn't be shooting much video after that.

In preparation, I thought I would buy some little packets of silica gel to throw into the camera housing to absorb any excess moisture in the air trapped inside. I armed myself with the word for "silica gel" (硅胶凝体) and paid a visit to the camera stores of Wangfujing Dajie, near my office.

It rapidly became clear that, whatever words the Chinese use for dehumidifying silica, it isn't 硅胶凝体. The girl at the Nikon showroom in Oriental Plaza gave me a funny look and said she wasn't too clear what I was asking for, even after I went through a laborious explanation that I thought would be clear to anyone working in a camera showroom (a substance that removes water from air to protect cameras in storage). The stores on the main street weren't much better, until I got to the third one. There, an attendant knew immediately what I was asking for and gave me the correct Chinese word for it (干燥剂, or "desiccant"). They didn't have any. Neither did four other stores I tried, although they all now knew what I was asking for.

Finally I found a store at the very end of the main shopping drag that had some. After much rummaging around in boxes and cabinets, they produced a tiny, little porous envelope containing two or three grams of silica, much the same as what you would pull from the bottom of a packet of Japanese rice biscuits. It came from next door, so for all I know they did pull it from the bottom of a packet of Japanese rice biscuits. It even had "desiccant - do not eat" printed on it, in English.

50 kuai each. How many did I want?

After my eyeballs returned to their sockets from a painful, Roger Rabbit-style aaaROOOgahhh!!! extrusion, I expressed my disbelief. And disbelief is the word. In Singapore I used to buy 1.5 kilos of the stuff for the same price. But the salesgirl, who had correctly worked out the "desperate+stupid=$$$" equation was not to be swayed. 50 kuai. Take it or walk.

I took it. At a stroke the saleswoman achieved the nirvana of Chinese retail. In selling me for 50 kuai an item with a wholesale cost of about a cent, she achieved as close to an infinite markup as is possible without actually selling something that is completely worthless  (the only reason why she wasn't assumed bodily into retail heaven at that moment, I figure). In fact, let's do some math. 50 kuai, or US$6.25 for three grams, equals US$58 per ounce. That's not far off the price of palladium, and probably the same as I'd spend on decent caviar. Caviar will not dehumidify the inside of a camera housing, though. I've tried.

The salesgirl painstakingly wrote me out a receipt, as if I might return my pathetic little packet if, say, it failed to absorb any moisture in Zhejiang. She did, however, give me a slight sneer when I asked for a small plastic bag. I guess she thought I needed the bag to carry three grams of silica, although the truth was I didn't want the silica absorbing moisture from Beijing's humid, summer air before I needed it. In fact, on the suspicion that the storage conditions had been less than optimal, I immediately microwaved the packet once I got home (which is how you re-set silica).

Beijing seems considerably less preocuppied with protecting cameras from humidity than Singapore. I suppose this makes sense. In Singapore, the humidity slowly destroys everything you own, including camera optics, which have problems with fungus. In Beijing, the dryness preserves everything indefinitely. If I'd made it to the big, professional looking camera store near Xizhimen I might have had better luck. But time was scarce, and I leave this afternoon. Next time I'll be better prepared. And even if this little packet of silica doesn't do the trick, I shouldn't be in too dire straits. I'm sure I can always find Japanese biscuits in Hangzhou.