Forging with a thin film of water on the anvil and hammer prevents forge scale or oxide from being hammered into the surface of the steel. The hot steel instantly vaporizes the water and the resulting steam explosion blows the scale off of the work, keeping it clean as it is worked. This type of bamboo scoop (竹の水差し, takeno mizusashi) is a traditional style tool for evenly applying water to the surface of the anvil or the hot steel.
Unlike steel, forge scale does not move or compress at forging temperatures. If a piece of scale is hammered into the surface of a blade it creates a depression and the entire surface of the blade will have to be filed down to remove the scale and pitting later. Water forging is one way to keep the blade clean and smooth and reduce work and waste during finishing and polishing. Swordsmiths usually keep a bucket of water right next to the anvil to supply water to the surface and to periodically dip the hammer into while working.
This is about the quickest and most useful traditional tool for controlled application of water, taking only minutes to create from natural materials. The best starting point is structural/timber bamboo that is about two inches inside diameter, is not cracked, and has at least one or two nodes or joints in it.
The photos at the bottom of this page show a thicker, striated grass-type bamboo, but the thinner and denser walls of timber bamboo (see photo above, as shown in the video) are the most efficient and longest lasting for this project. Bamboo culms reach their full strength in the third or fourth year after they emerge.
To begin, cut the bottom flush about 1cm (~3/8″) below the lowest node. Then measure a distance up from the bottom that is slightly less than the depth of your water bucket for the intake. Bamboo contain silica to strengthen their structural fibres which makes them tough on cutting tools.
Make two cuts about 5-10mm (~1/4″0-3/8″) apart (the width of your nearest sized wood chisel is fine) and just deep enough to cut through the wall of the bamboo, making sure at least the lower cut will be submerged at full depth. When cutting be aware that the bottom of the node dips down into the space below.
Use the wood chisel to remove the material between the cuts and clean up the opening.
Take a kiri or small drill and make a hole about 2-3mm (~1/8″) in the center of the bottom node for the outlet, start small and adjust it to your preference after testing.
Finally, skip one more node on the top if you have one and cut 1cm (~3/8″) above it, forming the handle.
To use the scoop, immerse the bottom in the bucket until the water rushes in the intake and then lift straight up and over the anvil while the water streams from the outlet. A variation of this design include making the intake a smaller rounded hole so that you can stop the flow by plugging it with your finger or thumb. Another is to turn it over and make another scoop from the handle end with a different sized outlet hole so you have two flow rates available (eg, a larger one for dousing the anvil between heats and a smaller one for applying directly to a large workpiece during forging). Some smiths use a small reclaimed drinking water PET bottle with a hole drilled in the top as a squeeze version of the scoop, though these must be opened and filled when they are empty.