To the bronze age index page

Reports about melting the bronze - 1997 and 1998

During 1999 I've continued our experiments, I've reported news on this page

Items
1. Ovens
2. Bellows
3. Charcoal
4. Crucibles
5. Bronze
6. Moulds
7. Technique.
8. Results
9. Extern advices.
10. Conclusion.
11. Plans
12. Additions to our knowledge
13. Latest news

A volunteer casting bronze in our Museum (a cire-perdue coin):

1.Ovens
The large oven that we used in 1996 appeared to be a bad one. It was too large, too much charcoal was needed and still the bronze didn`t melt.
When we made a smaller oven, it became hot much faster, less charcoal was required and everything worked much better. A nozzle dug in (about 45 degrees), pointing at the center of the oven.

2.The bellows
The size and shape aren`t very important. Just take care, that :
-they don`t leak
-the nozzle is placed well
-one must be able to continue the blowing without much effort
A 'shopping-bag' type of bellows worked very well and can reach a temperature of 1200'C!!

3.Charcoal
We sometimes use charcoal, collected after baking some pottery (a 'field oven'): 6 large baskets with a fine quality charcoal can be obtained that way...

4.Crucibles
Clay crucibles broke until we made thicker ones (> 0.5 cm) which we heated slower.
It`s not necessary to bake them before the melting process; they`ll bake during the pre-heating.

Late bronze and iron age tools: anvils, hammers, adze

5.Bronze
The best results were made with 'lathe-thrash'. That's a mixture of 'casting bronze' with 'phosphoric bronze' in fine splinters.
As it`s a mixture, the exact amounts of copper, tin and zinc can only be estimated; approx. 91% Cu, 6% Sn and 1% Zn (so in fact it`s gunmetal).
We succeeded 2 times in making bronze out of 90 % copper(-wire), 6 % lead and 4 % tin. In the meantime we have the disposal of 100 % pure tin!

6.Moulds
Various moulds give good results:
a.Casting sand

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                            

Method of making a mould for a socketed axe with the lost wax method: first a clay core, then the wax around it

7.Technique.

Some important conditions for melting and casting successfully.
Preparations.

• win all the information you can get
• good moulds and melting cups
• make efficient bellows
• hold tin, lead and /or pewter in reserve to lower the melting -temperature
• a basket dry charcoal
• obtain dry oak in chumps and chips
• use wet loam with straw to close the openings between the bellow-pipes and the oven-wall
• use 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 remain dangerous.
• put everything in its own place , so you don`t have to search when the situation becomes dangerous...
• write down as many details as you can , so the (good) results can be repeated.

The most effective procedure is:

1. to dig a pit and build an oven with half-wet loam
2. place the bellows
3. place the clay or loam moulds near the fire (but not to close)
4. reduce the opening of the nozzle when necessary
5. make a fire in the oven
6. put small pieces of charcoal over the fire
7. to pre-heat, place the crucible carefully on top of the charcoal (don`t blow!)
8. after pre-heating, start to blow until the crucible is red-hot
9. put the bronze in and lower the position of the crucible (the glowing charcoal gives less support, so the crucible might fall over)
10. put the charcoal over the crucible
11. blow approx. 20 minutes with the bellows
12. put more bronze in the crucible and charcoal over the top of it.
13. blow 10 minutes with the bellows, put on some sort of glove
14. pull the charcoal out of the fire, keep blowing
15. get the slag out of the crucible and stirr the bronze to test the fluidity
16. (if necessary for a harder, sharper result) add flux like tin and/or lead (lime? FeO/iron oxide?)and stirr
17. grip the crucible and cast
18. do you need a hard result : let the bronze cool down SLOWLY
19. do you need a soft / forgable result : let the bronze cool down in cold water

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.

8a)results 1997:

• 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' bracelet

8b)results 1998: (until October):

• 3 axes
• small anvil
• bracelet
• long dagger
• flat axe
• 3 "chickens"
• chisel
• 2 arrow-heads
• 3 needles
• 4 bars

Casting bronze axes by Ernest Mols:

9.Extern advices.
Now and then we read or hear about possible improvements.
A few are selected here :
-grind shells (lime!) and use them as a flux
-use ferro- oxides as a flux and to thicken the slag

10.Conclusion.
We learned a lot about the techniques and moulds in 1997. But still a few questions remain:

• our moulds and crucibles don`t last long, how did the ancient smith solve that problem?
• how can one grip the hot crucible with wooden tongs?
• what are the secrets of forging?

12.Additions to our knowledge
(February 1998)

We 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. We have also tried it out 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"

(Summer 1998)
2 Swiss women said they also casted bronze while there was snow. So now we knew that we could also cast in the winter.

(December, 6th 1998)
We casted bronze while there was 5 cm snow. The result was great; we casted 3 daggers...

13.Latest news about the experiments "bronze melting and - casting" in our museum

(April, 4th 1999)
After experimenting with soapstone we were surprised, not only about how easy it could be carved, but also about the pyro-technical properties. It's a pity there haven't been found any soapstone moulds (yet?) in the Netherlands. But we'll experiment with it, anyway.

Visit all our happenings in 1999!!!
You can visit us each first Sunday of the month to watch our attempts!
In 1999 we also try to cast an urnfield knife, probably looking like the knife below right:

Length: 144 mm, width 24 mm, weight: 95 g. Dating: 2800 - 2700 B.C.