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Index Dutch bronze age
Index first farmers in the Netherlands
Items 1.Ovens 2.Bellows 3.Tools 4.Charcoal 5.Crucibles 6.Bronze 7.Moulds 8.Technique 9.Results 10.Extern advices 11.Conclusion 12.Plans
a.dig a pit b.change the position of the crucible (a long pair of tongs with flat or bent mouth) c.change the position of the charcoal (see 'b', or a spoon) d.add more bronze (or flux!) to the crucible (a small iron spoon with a long handle) e.get charcoal and/or slag out of the crucible (see 'd') f.test the fluidity / stir (a bar, forged to a rectangular spoon) g.seize the crucible to cast (see 'b') h.protect the hands against the heat (e.g. a piece of leather or a bag with a hole in it for the thumb - a glove) i.forge (hammer, short tongs with a flat mouth, anvil) j.finish the bronze (whetstone, files, drills)
Advantages:-the mould can be made and used instantly
-it`s all re-usable
Disadvantages:-it`s hard to use the good amount of oil
-special 'sharp' sand is needed
Advantages:-fairly quick ready
-cheap
Disadvantages:-not re-usable
Advantages:-the loam fits perfect
-it`s re-usable
Disadvantages:-it`s fragile
Advantages:-quick
-re-usable
Disadvantages:-casted bronze oxidises fast, so a lot of work is needed afterwards
Advantages:-re-usable
Disadvantages:-it takes a lot of work
Advantages:-the finest details will occur on the result
-the result is unique
-extremely complicated bronzes can be cast this way, even hollow models...
Disadvantages:-it all takes a lot of time and effort
-the mould is not re-usable
-wax is expensive
-to dig a pit and build an oven with half-wet loam -place the bellows -place the clay or loam moulds near the fire (but not to close) -reduce the opening of the nozzle when necessary -put a fire in the oven -put small pieces of charcoal over the fire -to pre-heat, place the crucible carefully on top of the charcoal (don`t blow!) -put the bronze in and lower the position of the crucible (the glowing charcoal gives less support, so the crucible might fall over) -put the charcoal over the crucible -blow approx. 20 minutes with the bellows -put more bronze in the crucible and charcoal over the top of it. -blow 10 minutes with the bellows, put on the 'glove' -pull the charcoal out of the fire, keep blowing -get the slag out of the crucible and stirr the bronze to test the fluidity -(if necessary) add flux like tin and/or lead (lime? FeO/iron oxide?)and stirr -grip the crucible and cast -do you need a hard result : let the bronze cool down SLOWLY -do you need a soft / forgable result : let the bronze cool down in cold water9.Results
1 small chisel/ hanger 11 arrow-heads 3 needles 1 spear-head / knife 1 bracelet 1 chisel 3 hangers 1 brass axe various short bars 1 'cow' 1 arrow-head (tin) 3 'lunas' (hangers) 3 brooches 2 spear-heads 1 flat axe 1 female fertility idol 4 daggers 1 15 cm long bar 4 small palstaves 1 'horse' bracelet10.Extern advices.
Some important conditions for melting and casting successfully.
Preparations.
-win all the information you can get
-good moulds and melting cups
-efficient bellows
-hold tin, lead and /or pewter in reserve to lower the melting -temperature
-two baskets dry charcoal
-dry oak in chumps and chips
-wet loam with straw to close the openings between the bellow-pipes and the oven-wall
-wet loam to rub in the arms against the heat
-good tools to arrange the fire, and to hold the cup
-buckets with water and sand ; fires stays dangerous.
-put everything in its own place , so you won`t have to search when the situation becomes dangerous...
-write down as many details as you can , so the (good)
result can be repeated.
During the attempt.
-make a high fire with the oak-chips and lower it with charcoal
-place the cup with copper, bronze or brass (no tin!!) close to the bellow-pipes on a flat stone or on the charcoal
-surround the cup with charcoal
-put one piece of charcoal ON TOP OF the cup
-heat the moulds until 150'C ; they must become total dry
-write down what you`re doing and the time, so the situation can be repeated
-you can cover up the furnace a bit to remain the high temperature
-keep the heated area as small as possible , that saves coal and time
-about 10 minutes before the casting : put 3-10% tin in the cup. Is the mould laying solid and horizontally?
-Take the charcoal out of the cup and cast.
Afterwards.
-write down the results
-hold the casting in water (if a forgable result is needed !)
-put the fire together and put some sand over it.
(Feb 1998) We recently discovered a striking detail about loam. Normally one has to pre-heat the clay crucible before it can be used to melt bronze. If not, the chance is big the crucible will burst or even explode (when it's too wet).
But if one puts wet loam on the outer surface of the crucible, it can be put straight into a normal camp fire !!! The loam won't burst, but bake. But we haven't tried it out yet with the use of bellows.
The founder of Aubechies (a prehistoric site in Belgium), Léonce, gave us this advice.
His explanation of this strange effect was : "The loam will absorb the thermal shock"
Latest news about the experiments "bronze melting and - casting" in our museum
(March 1999) Last year we weren't able to cast an urnfield knife in 1998 (watch picture below right), but we'll prepare to cast it in 1999. We learned a few things last year. About the furnace: -make a loam "ash tray" on one side of the furnace to hold the hot charcoal during the casting. -When building a new furnace, try to include a place to heat the moulds in your design. It mustn't be to close, neither to far away from the fire. You could make some sort of "balcony" filled with a mixture of sand and charcoal or pottery shells. -Try to save your furnace for a next time by filling it up with sand, charcoal and old moulds. This way others can also see the purpose of that "strange place". -putting an open mould on the bottom of the furnace might be useful, but only if the furnace is shallow. About the moulds: (loam) -when putting a string around the double-sided mould, put a bit of loam on the small string to prevent it from burning. -don't pack in the whole mould with wet loam for 2 reasons: # it's too hard to separate the 2 sides after the casting # to let escape possible gasses -the ventilation canals don't have to be straight -single loam moulds don't work well -half-wet loam is very easy to work with, e.g. moulds for needles can be made that way (lost wax) Our ways in making a mould worked very well. But still some advices: -finish the wax off very neat because each line shows off in the result. -put grinded (wet?) charcoal on the wax before putting on the wet loam We 've also experimented in melting the wax in a high, small cup, then cooling it off with a wooden stick in it (which could be replaced by a piece of bone after the casting) But that didn't work well. A pre-heated iron bar could probably give a better result. And then cast it upside-down like on the image below. (misc) -put a small cup or pottery shell near the fire for the casting remains; never let the bronze cool off inside a cup. About finishing the bronze: -loam moulds give results which need a lot of work -lost wax moulds give great results About casting: -grinded chalk shells didn't work well during our attempts, and neither did the grinded iron ore. Crucibles:
-grinding shells (lime!) and use them as a flux didn't work with us
-using ferro- oxides as a flux and to thicken the slag didn't work with us
-meagre the clay moulds with much chaff or dry sand
-put wet loam around the crucible (against the thermo-shock) and put it in the low fire
-Advice from Aubechies: make a mould from 80% charcoal and 20% wet loam (usable instantly!)-we haven't experienced it yet
Picture right: Some late bronze age findings (Schoonebeek, NL)
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Index Dutch bronze age
Index first farmers in the Netherlands