No, it's not something you dowse your body with before a hot date. Here's the explanation:
10. Oyster Powder.—Open the oysters carefully, so as not to cut them, except in dividing the gristle which attaches the shells ; put them into a mortar, and when you have got as many as you can conveniently pound at once, add about two drachms of salt to a dozen oysters ; pound them and rub them through the back of a hair sieve, and put them into the mortar again, with as much flour (which has been previously thoroughly dried) as will make them into a paste ; roll the paste out several times, and lastly, flour it, and roll it out the thickness of a halfcrown, and divide it into pieces about one inch square; lay them in a Dutch oven, where they will dry so gently as not to get burned; turn them every half hour, and when they begin to dry, crumble them. They will take about four hours to dry; then pound them fine, sift them, and put them into dry bottles and seal them. Three dozens of natives require seven ounces and a half of flour to make them into a paste weighing eleven ounces, or when dried and powdered, six and a half ounces. To make half a pint of sauce, put one ounce of butter into a stew-pan with three drachms of oyster powder, and six tablespoonfuls of milk ; set it on a slow fire, stir it till it boils, and season it with salt. This makes an excellent sauce for fish, fowls, or rump steaks. Sprinkled on bread and butter, it makes a good sandwich. But only use plump juicy natives in the preparation.
The source is this extraordinary book: