Bran (Suibhne), plaster, 2008

Ancient Technology

“Hardly any traces are left of the actual production processes which brought us the beautiful artefacts of the Bronze and Iron Ages, found all over Ireland. Trying to re-discover this ancient technology is a fascinating and visually spectacular journey, with the destination of a more sustainable way of making contemporary sculpture.”

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Casting History

To produce his work, Holger Lönze brings the Bronze- and Iron-Ages alive by using five thousand years old technology to cast small bronze sculptures in the lost-wax process. Appropriately, his studio is only two miles from Mount Gabriel where some of the oldest copper mines of North-West Europe are located. Often used in a journey or workshop context, he investigates the relationship of the local archaeology and landscape by working with charcoal-fired and leather-bellows operated pit kilns, often to produce archaeology-inspired work. Archaeologists have found little evidence of metal production sites other than charcoal deposits, mould sherds and discolouration of the ground, leaving much to be discovered by imagination and experimentation. But it is not only the archaeological aspect which interests him. Using local materials, sustainably produced charcoal and recycled bronze makes the process itself carbon neutral, offering sculptors and crafts people an environmentally sustainable, inexpensive and low-tech approach to producing their own sculpture or jewellery.

Holger is currently developing wood gasification equipment for use in his studio foundry to further reduce carbon emissions and to use waste products. A downdraft gasifier will convert wood shavings and pellets into clean burning woodgas. He already uses recycled metal and moulds made from regionally sourced clay and sand as standard practice.

Process of Bronze Casting | Sustainable Foundry Practice

Process of Bronze Casting

From Transient to Permanent Form

To make an object in bronze, first a mould needs prepared for the object to be cast: in the Bronze Age carved stone moulds were used alongside wooden patterns pressed into a mix of clay, sand and horse dung. Recent finds also point towards the use of lost-wax technology in theIron Age, a technique which remains in use for casting artwork to the present day. After the base metals are extracted from the ore in the long and energy-consuming process of smelting, they are blended into a base mix of 90% copper and 10% tin. These ingots are then heated in a ceramic crucible within a small clay-built pit-furnace. Ordinary barbeque lumpwood charcoal is used in combination with a pair of simple valveless bag bellows that produce a constant flow of oxygen in order to reach the required temperature of c. 1050ºC. Once molten, the metal is poured into the prepared moulds, which are then broken open. After cooling, the work retrieved and finished.

 

The Lost Wax Process

There is reliable evidence of the lost wax process in Ireland dating back to the Iron Age. The technique gives the maker and artist more creative freedom than any other casting technique. The process involves making an original pattern of the work in wax, today a mix of beeswax, synthetic waxes and resins. After adding a runner and riser system, the work can be degreased and moulded. Various molding techniques are available to the sculptor. Bronze and Iron Age moulds are made of aggregate, binder and fibrous material: sand, clay and dung. The mould material can be applied either by dipping in slip form or direct application of a buttery paste. The latter has the advantage of faster drying times but the wax is more likely to be deformed during application. The former requires drying between consecutive dips, which can be accelerated by using a drying cabinet. A mould thickness of 1/2 to 3/4 inch is sufficient after which the wax is melted out, first by blowtorch then in a kiln below 200ºC. Setting the moulds on a water-filled baking tray with a drying rack or grid will help to retrieve 60% to 75% of the wax. The mould needs to be fired after melting out. Bisque firing to 600ºC for two to three hours is sufficient. An inexpensive flat-pack kiln is ideal for both these processes. The moulds are then wrapped in clay covered hessian and poured cold. This research is summarised in a downloadable/printable two-page Casting Tips PDF file.

See also the Bells page, the Bronze Horns page and the Gargoyles and Angels project website which gives an overview of all stages of the process.

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Holger Lonze making a Bronze-Age horn
Straw for the horn core Straw core for horns Core for horns Horn cores drying Samall handbells just cast
Making a core for a horn Adding willow to the core Binding the willow Casting a handbell  
Wax for a handbell Bell moulded Wax for bell coated in ash Bell moulded Bell moulded
Bell moulded Bell moulded      
         

Stages of the Casting Process

A selection of images from workshops, symposia and casting sessions to illustrate the process. Follow the process from top left to bottom right. Please roll over the images to enlarge and to show description.

 

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Sustainable Foundry Practice

Sustainable Casting Methods

With his unusual approach, Holger addresses environmental issues surrounding the production of art and design objects and metal work in general. The Bronze/Iron Age technology used for producing work takes the process from a highly specialised industrial and high-tech settings to a low-key studio environment or to a community event level. Rather than relying on mineral oil based fuels, long transport ways and imported materials, the process instead facilitates local regenerative and recycled materials such as charcoal, clay, horse dung and sand. Some of the beeswax is locally sourced. The low carbon process produces little waste nearly all of which is recycled. The environmental impact will be further reduced by using wood gasification soon. Owing to the high durability factor of the resulting work, the outcomes offer a very low embodied energy value (115-180 MJ/kg for the metal and 2-10MJ/kg for all other materials used) throughout their life cycle. Recycled bronze is used together with local or FSC approved charcoal and abundant sand and clay. Up to 75% of the wax and 90% of the mould material are retrieved. This keeps the total embodied energy input in the actual production process very low.

Throughout the process, Holger is mindful of the environmental impact of the methods used in reproducing artwork. A basic analysis is used to evaluate this impact, which takes into consideration:

1. Distance to source of consumables (clay and sand are locally dug)
2. Abundance of consumable materials (regional charcoal and wood waste)
3. Embodied Energy Value (EEV) in MJ over whole lifespan in MJ/year
4. Recycled fraction of materials (high: reclaimed bronze; wax and moulds are recycled)
5. Cyclicity (any waste is reused and castings can be remelted)
6. Production of emissions/waste (low with the whole process)
7. Production of toxins in the process (low)
8. Recyclability of product/cyclicity (fully recyclable)
9. End-of-life waste
10. Total car transport (medium as regionally sourced)
11. Any other impact

The process brings together issues of sustainability, low cost materials, local history, specialised processes and spirituality: in an ephemeral process, fire, water, air and earth are combined to produce small works of art that can last thousands of years.

See also: Ethnoarchaeology in India

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