SAND CASTING IN NEPAL

To light the furnace, some drops of petrol on a few charcoals in the bottom of the furnace are set aflame. Very little air is given until the charcoals glow, then a graphite crucible is rested on them and more charcoals go between the crucible and furnace walls. Some small pieces of charcoal are placed inside the crucible, on top of the scrap metal, their reducing action making the use of flux unnecessary. Sometimes the crucible is capped with a bigger piece of charcoal over its mouth.The air blower can now work full blast, raising the temperature of the crucible until the metal melts down.Scrap brass comes from dishes, nuts & screws, flanges, taps, and so on. If a piece of brass is too big to enter the crucible it is warmed on the furnace and broken hammering it on a stake embedded in the ground in front of the furnace just for this purpose.

brass breaking

If the brass is too hot, though, it will bend instead of breaking. Medals, pendants and statuettes require a warm-colored, softer brass alloy; a whiter, harder alloy is preferable for dies and punches. To judge the quality of the alloy, a little molten metal is picked up with an iron spoon and dropped in water. Its color is checked, if too light-colored for the purpose, copper is added; if too dark, German silver is added.

Jugendra's commissions range from production and retail work to brass work for the army and one-of-a-kind pieces, mostly employing the sand casting process. Sand castings are carried out in a shed 5 ft. wide, 5 ft. deep and 7 ft. high, made of unbaked bricks bound with mud as mortar. It has a door and two very small windows, light is scarce. Between the walls and the roof of corrugated iron there are gaps to let fumes out, as there's no hood and chimney over the furnace. The furnace is built with bricks and muddirectly on the floor; their soil is very clayey. During the night this shed houses, under a basket upside down, a hen and her chicks.White sand is collected from the shores of a nearby river and is sifted a little at a time using a silk cloth as a mesh. The freshly dug white sand is mixed with burnt sand and dampened with a water solution of molasses. The grains of sand having been rounded by rolling in the river are not sharp enough for water alone to bind them. The sand is kneaded at first by hand and then by feet, in an iron pan; should the sand be too dry, a little solution of molasses is added; if too damp, it is set to dry in the sun.

To prepare the mould, the drag (the lower flask, without pins), resting on a wooden board, is filled with sand that is pressed level using the other board.
The flat surface is dusted with French chalk, the model to be reproduced is laid about one inch from the pour and pressed into the sand, completely if flat-backed, only halfway if three-dimensional.

The model in the drag is chalked; the cope (upper flask) is fitted upon the drag and filled with well loosened sand.

model flinging This is leveled with the board and pressed somewhat harder with the thumbs directly over the model. The depression left by the thumbs is filled in excess with sand, then the board is rubbed in a circular way to distribute the sand and pushed to level it. The board is then lifted and banged flat on the cope.The flasks are turned over, the board on the drag is lifted, the sand over the model is pressed with thumbs, the depressions filled, the board again dragged, pressed and banged once more. I don't know if this banging has some useful purpose or is a kind of satisfactory comment on a well-done job. Now the flasks are opened carefully; the model remains embedded in one of the flasks. This flask is held in the left hand; a few taps on the model dislodge it. To get it out without spilling the sand, the flask is set in a fast upward motion and abruptly stopped; the model flings out to be caught by the right hand.
Should the model be too large, the sand could fly off with it, so a different procedure is followed. After the dislodging taps, a finger is placed in the center of gravity of the model and kept there while carefully turning the flask over. A quick lowering of the hand lets the model fall into the palm.
In both halves a funnel shaped pour for the metal is made by a deft passage of the thumb, removing the sand between the top of the pattern and the opening of the flasks. The cross section of the tapering pour at the point where it meets the model is somewhat thinner. This makes it easier to remove it when the cast is cold enough to be handled. Most of the time holding the cast with one hand and bending the pour to and fro with the other, will make it break at the right point.

pouring Both halves are checked for imperfections and carefully closed. Small flasks are held in hand during the cast, bigger flasks are rested on the floor and held against the furnace's outer bricks with an iron rod.When the metal is molten, charcoals are removed with the tongs; smaller charcoals and ashes are blown out of the crucible with a pipe. A tiny piece of aluminum is thrown in the molten brass just before pouring; it has a reducing action. For small casts the crucible is not lifted from the charcoals, instead an iron spoon is used as a small pouring ladle: it has a long iron handle and the bowl bent on the left. After removing the charcoals from the mouth of the crucible, the spoon is dipped into the molten brass and retrieved carrying the quantity of metal needed for one pour. The spoon wears out with use, small holes are usually patched with a pinch of moistened clayey soil from the floor, the spoon is then set near the fire to dry, and is ready to resume pouring.Pouring is very smooth. A few seconds after pouring is over, the flasks are tilted over the spoon to recover what sprue metal has not yet solidified to put it back in the crucible. The iron spoon is laid on the embers to keep it warm, the flasks are opened, and the cast and surrounding sand are removed. Later the burnt sand is thoroughly dried, hammered and sifted through the silk cloth,then added to fresh sand; this mixture works better than fresh sand by itself. Generally one load of the crucible is enough for the planned casting session. The crucible sinks as charcoal burns off, it is lifted back level and new charcoals are put under it; care is taken not to overheat the metal or let it cool down.

Most models include the sprue so there's no need to carve one in the sand. Projecting parts of the model have a feeder to ensure a complete cast.

Silver melting is undertaken with great care, a smaller furnace is used, made out of a tin can formerly containing ghee (a kind of salted butter). It is roughly cubic, 1 ft. high; its interior walls are lined with sand and clay. One small crucible is refilled after each pour, so that the silver melts down while the next impression is taken in the sand. Fine silver does not flow well, so it is necessary to add a little copper to it, never exceeding 5% of total weight. In this case a pinch of borax is thrown in the crucible.

wavy surface of sand model & cast ring

Rings are cast straight and bent afterwards; but the head or bezel being thicker is not straightened . So while pressing the curved pattern in the drag the sand is made to follow the pattern's elevations: the cope's sand will adapt to the wavy surface of the drag sand.

To cast spoons, statuettes and such, somewhat bigger flasks are employed.
They are uneasy to handle, so to ensure a better grip, the parts of drag and cope which touch the board, are widened, the sides sloping towards the parts that interlock.
The tip of the fingers can rest on the slant of the sides with no risk to let the flask slip. Moreover when the drag is turned over to let the model drop down, the mass of sand is kept inside a kind of inverted funnel and is less likely to fall.

To cast hollow statuettes a brass plug is used as a false core, protruding from the statuette's bottom roughly as much as it goes inside it.

First one impression of the statuette and plug together is taken, the flasks are opened and the statuette and plug extracted.
The pour is carved.
The plug is warmed in the furnace and replaced in the sand with tweezers, the flasks are then closed and metal is poured.

If the plug were not heated, it would cool the incoming metal and the cast would be incomplete, moreover the plug would not shrink in cooling, causing cracks in the shrinking cast.