The ancient rules of monastic discipline specify that a Buddhist monk is required to own an alms bowl made of earth or iron, and that this bowl is to be baked in a fire from time to time. The commentaries state that an earthen or clay bowl should be baked at least twice, and an iron one at least five times. One of the skills that any junior monk should learn before becoming free of dependence on a teacher, along with sewing and dyeing robes, memorizing (and following) the Pātimokkha, and of course meditating, is the art of bowl baking.
However, most alms bowls aren't baked any more, and the art seems to be dying out. When I first came to Burma more than twenty years ago, clay bowls were already rare, and the "regulation" monk's bowl sold at Sangha supply stores was pounded, so I was told, out of the bottoms of 55 gallon oil drums and then coated with black lacquer. Over the years fancier bowls became more and more common, a typical model being made of iron or steel and somehow processed with a matte black finish very like that found on military hardware. Expensive stainless steel bowls imported from Thailand are becoming almost the standard; and some Burmese monks, and apparently most Thai ones, leave the shiny stainless steel unbaked and unblack.
Some years ago a book on Buddhist monastic discipline in the English language was published, which seemed to imply that to bake a bowl one simply sticks it into a fire. However, this would certainly not prevent an iron bowl from rusting, nor would it turn it any blacker than it already was. Bowl-baking involves coating the bowl with an enamel-like black finish that prevents iron bowls from rusting, and presumably would prevent clay bowls from being porous enough to absorb liquids from the monk's food, and thus would prevent them from becoming stinky and gross.
Even though most Western monks nowadays seem to use stainless steel bowls that are immune to rust, still it may be useful to monks who wish to follow the ancient ways, to see a method much used in Burmese forests for baking an enamel coating onto a bowl. It also may be useful to a few artsy-craftsy type laypeople who would simply like to know how to cover implements with a glossy black finish that was favored in ancient India before the invention of spray paint. Anyway, here is the method. The entire process, not including the cooking of the oil, takes about two hours or a little less.
You will need:
~at least one alms bowl
~about half a cup of sesame oil
~an old can to cook it in
~some steel wool, emery cloth, or similar abrasive
~three big rocks or about nine bricks
~three small flat rocks or three smallish potsherds
~a piece of sheet metal about two or three times as wide as the bowl to be baked, and wider than the next item
~a metal bucket, pot, or other receptacle large enough to invert over the inverted bowl without touching the sides
~at least two potholders or thick, folded or wadded cotton cloths (not synthetic, silk, or wool) for handling very hot bowls
~enough firewood to keep a medium-sized fire going for a few hours
~a clock or watch
Step 0: Preparing the oil.
The sesame oil should be cooked over a fire until it is blackish sludge. When still hot it should have the consistency of chocolate syrup, and after it has cooled it should be about as thick as sweetened condensed milk. If it's too runny it will run down the sides of the bowl before it sets, and if it's too thick it is hard to spread it thinly.
The trick for cooking the oil quickly is to let it catch fire – consequently, it is best to do this outdoors over a fire, like the rest of the process. If the oil catches fire it may be ready in half an hour or so (depending on how much of it one is cooking); but if it doesn't catch fire the cooking process may take about two days. It was many years before I learned this important trick. One should start with about twice as much oil as one intends to wind up with, as some of it burns away. After preparing the oily sludge it can be kept for years, so it's good to prepare extra for future use.
The fast way of cooking oil
Enough cooked oil for two or three bowls
Step 1: Simply stick the bowl into the fire.
This step may be skipped if the bowl to be baked is plain, unfinished pottery or metal. But if there is old enamel, spray paint, or some other coating on it, it should be burned off in the fire. Dead leaves or other combustible debris may be put inside the bowl to help the inside burn also. Then it should be allowed to cool.
Burning off the old coating
Step 2: Clean the bowl well.
If the bowl was burned in the fire and has rust or burnt crust on it, it should be rubbed smooth with some abrasive. Steel wool works well. If a little of a previous baking's coating still remains, or if an iron bowl has a reddish tint from rust, so long as it's smooth there's no problem. At this point even a new bowl should be washed and rinsed carefully, so that it is clean, bare pottery or iron.
Incidentally, I once asked a monk friend of mine how the rust was removed in ancient India, before the invention of steel wool and sandpaper, and he said they used a kind of strong vinegar to dissolve the rust. This supposedly had been used in Burma in the old days also. But I'm not sure if vinegar really dissolves rust, and guess as an alternative that they simply rubbed the bowl with sand, or pumice, or something.
Step 3: Smearing the oil onto the bowl.
The trick with smearing the burnt sesame oil onto the bowl is to smear it as thinly as possible. If the black coating on the bowl has little cracks after the bowl is baked, and/or if the rim of the bowl has a crust of semisolid oil that flowed down the inverted bowl while baking, then this is a sign that one has spread the oil on too thick. (Such a bowl is still usable, however.) A good method is to dip one's finger(s) into the oil, and then make little dabs of the oil all over the bowl, and then spread it out in a uniform layer. Again, spread it as thinly as possible, using the oil sparingly, yet of course leaving no spot unsmeared. Smear the inside first; it's easier that way.
Smearing the Bowl
Step 4: The actual process of baking.
The piece of sheet metal is set on the rocks or bricks with maybe a foot of clearance with the ground, and the fire is maintained underneath. The flat stones or potsherds are set in a triangle of adequate size to place the inverted bowl onto them so that it doesn't come in contact with very hot metal. The bowl is placed upside-down onto the stones or potsherds, and then the cover is placed over the bowl. At this point one should note the time.
If the fire is small, one round of baking may take ten minutes or more. If the fire is medium-sized, it may take as little as five or six minutes. If the fire is a roaring big one, the coating will bake on and then promptly burn off again, requiring one to start over. This can be very frustrating when one has already done three or four rounds, with three or four layers baked on, so it is best not to have a big fire.
One should watch the smoke coming out from under the receptacle covering the bowl. After a few minutes smoke will be emitted, and then after a while it will stop. When the smoke stops, the bowl is done, and should be removed from the fire to cool. If the smoke stops and then starts again, that means that the baked oil is now burning off – that is not a good sign. Because it is difficult sometimes to gauge the smoke emissions, a clock is handy. The bowl should be checked after five minutes or so; if it is smoking a lot, or if it is still sticky, it's not done yet. To leave it just a little smoky or sticky is allowable, and much preferable to overbaking.
Some monasteries in Burma have a bowl-baking cover with a hole in it, to facilitate observing the smoke coming off the bowl. If the emitted smoke can be clearly watched, then a clock is unnecessary.
Different bowls will have different optimal baking times, depending largely upon their thickness and mass and what material they are made of. A thick iron bowl will take longer to bake, and much longer to cool, than a thin stainless steel one.
After removing the bowl from the fire it must be allowed to cool enough to be handled before applying the next coat. Consequently, it is just about as easy to bake two or three bowls as it is to bake one: while one is baking, another is cooling, while a third may be receiving its next coat of oil. Although a bowl may be baked by one person, two monks have an easier task than one, with one tending the fire and removing the cover and the hot bowl from the fire, and the other smearing the oil (with oil all over his hands). Whoever tends the fire should try to maintain it at a uniform size, and not too big.
Step 5: Baking it again and again.
As mentioned previously, the commentarial tradition advises at least two bakings for a clay bowl, and at least five for an iron one. Repeating Steps 3 and 4 above results in a layering of enamel, which causes the finish to be sturdier and to last longer. After the fifth baking, an iron bowl should be a beautiful glossy black. It should be washed before food is eaten from it.
Some monks with steel bowls bake only the outside for looks. (Recently I was informed that some wiseguy monks in Thailand smear their $200 stainless steel bowls with eucalyptus oil instead of sesame, to give them a luminous, iridescent finish.) The enamel tends not to adhere as well to stainless as to pure iron. Metal bowl lids may be baked this way too.
The sesame oil enamel is rather sturdy, but still one should be careful about scraping the bowl with sharp implements like forks while eating from it, and should not use strong abrasives when washing it. The coating on a well-baked alms bowl should last for two years at least. A mediocre job will last a year. A bad job, as with a bad life, is to be done again.
The method described above, or so I've been told, is a standard method imported into Burma from Sri Lanka long ago, but there are other methods. I visited one monastery in Mon State in Burma where they didn't cover the inverted bowl while baking it; they used a cauldron, so the heat surrounded the baking bowl on three sides at least. But even uncovered like that would probably be more sophisticated than the way it was done in ancient India by wandering ascetics. I've been told that it is possible to bake a bowl by carefully placing it very near a fire and occasionally rotating it so it bakes one part at a time. I assume this was the original way. It probably would be pretty rough, and not so pretty to look at, but at least it wouldn't rust.