Casting, an age-old tradition, has been an inseparable part of sculptural and form-making methods for thousands of years, and its importance hasn’t diminished with the development of new materials. From functional products to intricate sculptures, casting plays a vital role in manufacturing and art.
In this article, we delve into the world of African casting tubes, exploring their uses and the unique Ashante casting technique. This method, originating from West Africa, offers a fascinating glimpse into the ingenuity and artistry of the region's metalworkers.
Lost-wax casting process
Understanding the Basics of Casting
Mouldmaking/casting involves covering the object you want to copy in a material which will then become firm enough to be detached from it and keep its shape, so that a hollow space or negative of the object is left. It means for example that a form can be modeled in a material which makes modelling easy, such as clay or modelling wax, but which can then be transformed into something permanent such as metal or concrete. The most effective and most used flexible mouldmaking material today is silicone rubber which can either be poured as a liquid or (with a special thickener) brushed as a paste on the surface of the original object.
The mould can then be filled with a casting material to make an exact replica of the shape. If it is poured as a liquid, temporary walls of cardboard or clay need to be set up around the object to contain the liquid rubber while it sets. Many different forms of object can be reproduced in this simple way by just creating a block mould of silicone around them as long as they have one flat side which then becomes the entry or pouring hole of the mould.
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Also, during the process of creation, sculptors may wish for a way of ‘saving’ an important stage in their work, rather like one can on the computer. Although more time-consuming, being able to make a cast will achieve just that! It’s also worth bearing in mind that the same can apply to forms created by 3D printing.
It’s probably fair to estimate that at least 90% of the things we use in our daily lives have relied upon some form of casting for their manufacture. If you are, or intending to be, a prop-maker or model-maker, it is a fairly essential skill to have.
Even though the form itself will be no surprise, it feels like making something new. With more practise it’s not hard to produce your own sculpture edition i.e. a series of casts, or it may open up ways of manufacturing your own functional product. Everyone I’ve tutored so far has experienced a strong sense of achievement in making a successful casting, even if the original form is ‘found’ i.e. not of their own making. It’s curiously exciting, unpacking a mould for the first time to see how a cast has turned out.
The Ashante Casting Technique
In 1965, while visiting near Kumasi in Ghana, Max Frohlich first saw the process of Ashante casting. At the time he was serving as "external assessor of exams" at the university in Kumasi.
Ashante casting (also spelled Ashanti and Asante) is a lost-wax gravity technique which is similar to the foundry-style casting of today. The distinguishing aspect of the Ashante process is that it is "closed-circuit." Most lost-wax gravity casting is done by pouring hot metal into a clay mold. In the Ashante process, however, the metal crucible and flask are one unit.
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This entire unit is fired up to the flow point of the metal within and then inverted to allow the molten metal to pour into the wax cavity. There is no direct pouring of metal into an open flask; neither is centrifugal force used.
This method is particular to the people of the Ivory Coast, Ghana, Nigeria, Benin, and Cameroon. Sub-Saharan Africa has an environment rich in natural resources for making models and the outer clay coating. Hardwoods serve as fuel for firing. Naturally occurring gold deposits have been used not only to fashion objects but to attract trade as well.
Although lost-wax gravity casting with bronze was in use around AD 1000, there is no hard evidence to indicate when closed-circuit casting began. It is also unclear whether closed-circuit casting arose from within this region or was introduced from outside. A century prior to European contact, West Africa had established trade routes reaching as far east as India, where the technique may have originated.
As trade with the Europeans increased, so did local mining. By controlling trade and the gold fields, the Ashante became the most powerful state of the Akan peoples, with the Ashante king amassing great wealth for the state. Gold dust was used as currency, and goldsmiths became a privileged class. The goldsmiths were responsible for the casting of jewelry and royal regalia. They also produced the cast brass weights and boxes by which gold dust was measured and stored. During the 18th and 19th centuries, production of gold and brass castings reached its peak.
Ashanti Brass Gold Weight
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Categories of Castings
The castings fall roughly into three categories: castings from nature, geometric images and representational imagery.
- Natural cast forms, for which objects from nature are cast directly, include shells, beetles, plant pods and seeds.
- Geometric images include flat discs up to 4 inches across, rectangles, tubes, hollow spherical beads and more complicated forms.
- Representational imagery includes human figures, animals and tools, serving to illustrate proverbs and scenes from daily Akan life.
Proverbs were in common use, both as a distillation of traditional wisdom and as a means by which the chiefs, priests, elders and spokesmen mediated between the king and his people. The use of such imagery has a dual purpose, combining utilitarian function with a method of conveying verbal concepts.
The castings are beautifully complex with rich detail. Smaller castings are generally solid, and ones larger in scale are hollow to conserve metal. These hollow castings can be extremely thin and free of porosity. The surfaces achieved are the result of highly skilled and proficient wax working.
Wax threads as thin as 26 gauge are rolled from beeswax using a wooden paddle, inverted board, palm oil and warm water. The wax threads are then tightly coiled or wrapped around clay forms to fashion beads, portrait masks and animals. Solid castings are often made by cutting or pinching wax into shape, and then further tooling this shape with a hot needle. Wax details are fused on as embellishment.
This methodology, although historical in nature, is still being practiced in West Africa today. Brass castings of weights, boxes and tourist items are commonly found in marketplaces in Ghana and Cameroon. Gold castings are usually reserved for commissions to the Ashante state.
Max Fröhlich and the Global Spread of Ashante Casting
What Max Fröhlich observed in Ghana in 1965 were contemporary expressions of Ashante casting using centuries-old forms and techniques.
In order to inspire other goldsmiths and to point out the technical virtuosity of Ashante casting, he published a paper on the process in 1975. In 1977, Fröhlich returned to West Africa, this time to the grasslands of Cameroon. While there he was asked to help with technical problems of porosity in brass castings. He was able to share information he had gathered from the goldsmiths of Ghana with their counterparts in Cameroon.
His analysis of West African casting allowed Fröhlich to establish a European equivalent of this technique and continue his commitment to sharing information. He and his wife, Ruth, conducted workshops in Ashante casting in various schools in Switzerland, Germany, Austria, the Netherlands and England. "I thought it could be interesting for goldsmiths and sculptors to cast in this way," he said. "Perhaps it could be a way of working for us."
Ashante casting made its way to the United States in 1986, when Max and Ruth Fröhlich hosted their first workshop at the Haystack Mountain School of Crafts. In 1991 they returned to Haystack, where they worked tirelessly with a class of professional metalsmiths and advanced students for two weeks.
The Fröhlichs then gave lectures and demonstrations at the Tyler School of Art and the Cleveland Art Institute. Haystack provided an environment with the intense sense of community found in a casting village. In the shanty that housed the two handmade kilns, Max Fröhlich would squat at eye level to the kiln in use, as he had done in Africa, to read the subtleties of the fire. Ruth Fröhlich would carefully mix investment clays and knead them to the correct consistency.
Teaching was by example rather than words, and very few motions were wasted. Almost 90 castings were made, from small intricate beads to large hollow vessels and wall pieces.
Process Overview of Ashante Casting
Ashante casting, as adapted by Max Fröhlich, requires a series of detailed steps. Some of these can be dangerous unless proper safety precautions are used. In particular, one should be aware that brass casting produces toxic zinc fumes, necessitating the use of a respirator and outdoor firing. The following description is not meant as a teaching guide but only as an introduction to the process.
Perhaps the most important part of the Ashante technique is making the wax model, for it is here that one begins to exploit creative possibilities. Raw beeswax is traditionally preferred because of its ability to be worked into thin sheets or wires. Commercial waxes, although more brittle, may also be used. The wax can be worked simply with the aid of an alcohol lamp, spatula and needle tool. Parts can be welded together with the heated tip of the needle tool. When the model is finished, wax sprues must be added to form a vent for the release of gas and a passage for the metal to enter the mold. The wax model, once weighted, is ready for investment.
Invested waxes ready to be closed in and eventually fired
There are two clay bodies used in the investment process.
- The Fröhlich charcoal clay, used as a face coat around the wax model, contains 1 part fine grog and 1 part charcoal powder by volume, to which is added 10% bentonite by weight. These are thoroughly mixed with water and several tablespoons of alcohol to a creamy consistency. This must sleep for 24 hours before use.
- The Fröhlich clay, used as the outer jacket and crucible, contains 3 parrs coarse unwashed grog to 1 part fine grog by weight, to which is added 10% bentonite by weight. Chopped grass or organic materials are also added. These are mixed with spring water until the clay is the consistency of pastry dough. This must also sleep for 24 hours before use.
To begin investing, the wax model is painted with alcohol to encourage the charcoal clay to stick. While still wet, a 1-mm-thick coat of charcoal is dabbed over the entire surface. Second and third coats, each 2 mm thick, are then applied, with drying time allowed between each coat. The charcoal coat preserves detail and carbonizes the atmosphere around the wax model, preventing porosity.
Coating the wax model with the outer clay involves several stages. First, over the charcoal clay, a thin layer of outer clay is applied by kneading the clay into walnut-size lumps and pressing these onto the moistened form. This layer is about 5 mm thick and is allowed to dry until warm to the touch. Second, the sprue area is built up to form the bowl of the crucible and allowed to dry. At this stage the wax is melted out over a charcoal fire. Finally the sprue hole is covered with a wax pad, and metal pieces added to the bowl and covered with newspaper. The bowl is then closed in completely with clay, forming a bulb-shaped crucible. The crucible can be reinforced with one or two extra layers of clay. The entire flask should be dry before firing. The West African equivalent of this clay body is high in silica and feldspar. Mixed with cow dung, the porous clay has less than 1% shrinkage and resists cracking.
A 15-gallon garbage can of galvanized steel serves as the outer wall of the Fröhlich furnace. At the base of the garbage can is a vent hole 3 inches in diameter. The garbage can is lined with a fiber-fax insulating blanket and refractory brick, which is mortared into place. At the bottom of the kiln is an air chamber, above which is a perforated plate of cast refractory cement, forming a false bottom. When air is forced into the chamber at the base of the kiln, an upward draft occurs. The charcoal fuel is burned from the base of the kiln upward, and heavily insulated side walls help maintain temperatures which can reach 2200°F (1200°C).
Firing is perhaps the most enjoyable part of Ashante casting. The entire process depends upon one's ability to "read the fire." Subtle changes in the color of the flame, coals and smoke are indicators of temperature changes within the kiln. The fuel must be a hardwood charcoal such as oak, maple or mesquite. Hardwood charcoals yield a slow-burning fire, producing an oxygen-depleted environment within the kiln. Firing can take from 20 minutes to 2 hours, depending upon the size of the pieces to be cast.
To begin firing, the kiln is partially filled with charcoal and the flasks are placed crucible side down. After preheating for 15 minutes, small pieces of charcoal are rightly packed around the flasks, filling the kiln. The heat in the kiln is gradually brought up until a yellow-orange flame appears, the result of wax residue in the flasks burning off. An air source, either foot bellows or hair dryer, may be used until the coals at the top of the kiln are glowing. Periodically, the charcoal is tamped down and new charcoal added to the top of the kiln.
When the brass begins to melt, greenish-yellow flames are produced and a whitish-yellow condensation forms on top of the coals. Both of these indicate that toxic zinc fumes are being released. After the yellow-green flames subside, a white zinc smoke is produced, indicating that the flasks are ready to cast. The flasks are pulled from the kiln, drilled to release gas, and inverted to allow the molten metal to flow into the wax casting. The hot flasks are set aside for about 5 minutes until the metal solidifies. They are then quenched in water and cracked open to reveal the finished castings.
Opened flask with cast metal inside
For metalsmiths, Ashante casting provides many benefits. The establishment of a small foundry is inexpensive, costing less than $200, and easily managed by one person. Castings from the intimate scale of beads to larger hollow forms are all possible using the same setup. The castings can be extremely thin, with high-resolution detail in which something as subtle as a thumbprint can show in the finished piece. The surfaces of the castings require little finishing, and a variety of metals, such as brass, bronze, gold and silver, can be used.
Materials and Tools
Here is a list of essential materials and tools for mouldmaking and casting:
- Some form of covering for the work surface (i.e. baseboards (size depends on the size of form you are working with. The baseboard should be around 5cm larger on all sides.
- Reusable clear plastic measuring beakers (these are essential for mixing silicone rubber because they’re generally stronger. Available in different sizes, but I use medium-sized 200ml. Available from Tiranti).
- Mixing sticks (‘coffee stirrers’ i.e. from Starbuck’s, Costa’s etc. are fine for small amounts of resin. Disposable chopsticks are excellent! Larger, broader sticks are better for stirring plaster .. better than using spoons). Mixing sticks should either be thoroughly cleaned or kept separate (i.e.
- Digital weighing scales, as mentioned (mine is a Salter brand ‘Aquatronic’ which takes up to 5kg measuring in 1g increments, available online c.
- Disposable plastic pipettes may be needed (dependent on the brand of silicone used) for dosing small amounts of additive.
- White spirit and small brushes (you will need white spirit in case of silicone spillage. Uncured silicone rubber dissolves in white spirit.
Health and Safety Considerations
There are relatively few materials commonly used for mouldmaking and casting that pose serious health & safety issues, but those that do need special measures. Polyester resin for example should never be used in the home because firstly the build-up of styrene emissions is harmful and secondly the catalyst (MEKP methyl ethyl ketone peroxide) is highly flammable and even explosive! The clear version of polyurethane resin (different from the standard opaque versions) is a similar health hazard!
Dust-masks should be worn whenever handling large amounts of plaster or any other substance, such as a filler, which becomes easily airborne. Good ventilation is essential to dissipate the vapour from solvents such as white spirit or acetone, which are of course flammable but can also cause headaches/dizziness. It is essential to read and act upon the MSDS (Material Safety Data Sheet) for any material you are using.
Tips for Beginners
I’m often asked for advice from people wanting to make the most complicated moulds or casts before they’ve experienced even the simplest handling of the materials. For example, start by making the simplest kind of flat, 1-piece, open mould. Make or choose a prototype (the original form to be reproduced) which can be fixed down to a flat board, has an interesting amount of detail (to make the effort worthwhile) but fairly minimal undercutting.
Many complicated forms can be more achievable by making them in easily mouldable parts (each requiring just a simple mould) which can then be easily filled and the parts then assembled. The prototype pieces for this chair were cut and smoothed from 2mm Palight foamed Pvc and fixed...
Start by exploring what’s possible by making simple block moulds first.
Metal Casting
By understanding the materials, techniques, and safety considerations, you can embark on a fulfilling journey into the world of mouldmaking and casting. Whether you're replicating existing objects or creating original sculptures, the possibilities are endless.
