Mount making for freestanding stone sculpture
Image["Torso of Psamtik (Psammetichus) II"]
Several of our objects will be displayed outside the new showcases, on free-standing plinths of Portland limestone. But often these objects, like this statue of king Psamtik II ( E.1.1865), are broken at the base and so will not stand up properly without some help. To solve this problem, each free-standing object must have its own custom-made base to support it.
Fortunately, Bob and Louise, our technicians, have a good deal of expertise in this kind of work.
First the object must be turned upside down and supported. To do this it is placed inside a packing case with a great deal of packing around it. Great care must be taken to make sure that the object will be level it is placed on its new support.
Once it is upside down, the base is cleaned because a lot of our sculpture has the remains of plaster and even some paint marks from earlier displays. (You can see some of this on the bottom of the statue of Psamtik shown in the picture.) All these marks need to be cleaned off carefully using the right kinds of chemicals before the mount making can actually begin.
Next, a layer of cling film is laid over the objects base, so that none of the epoxy resin or plaster (which will be used to make the support) can seep on to the object itself. Then, using small squares of aluminium foil and parcel tape, a thin-walled mould is formed. Every small holes must be filled before pouring in the resin (or plaster) to the level that is needed.
Bob and Louise have been experimenting with different types of material for the support. Here you can see Bob mixing some epoxy resin to try out. It produces a lot of fumes, and so he is mixing it up inside a cupboard with an air extraction system (called a fume cupboard). The bright green gloves are to protect him from the resin too.
Then the epoxy resin is poured into the mould, where it foams up to fill the space. It takes 24 hours to set.
Image["Pouring epoxy resin into the mould"]
Image["Bob mixing epoxy resin inside the fume cupboard"]
An alternative material for the supports is a very hard plaster (Crystalline Alpha-K). The picture shows a mould made of plastacine, which Bob and Louise are also trying. Once the plaster has been poured in, it will again be left for 24 hours to set properly.Image["Mould made of plastacine"]
Once the plaster or epoxy resin has set hard, we have a perfect cast of the base of the object which can be taken off cleanly. The upper surface of the cast will be the part which will rest on the plinth, and so this must be completely flat to make sure that the object stands properly.
So the cast is 'milled' to make a flat surface using a special machine (called a milling machine). Then all the edges are neatly trimmed back, so that the object slightly overlaps the cast.
Finally the edges of the support need a thin coat of fine surface plaster (e.g. Polyfilla) which gives them a smooth finish, making them ready for painting with acrylic paints to make the plaster look as much like the portland stone plinth as possible.
So, when you see our some free-standing sculpture on a plinth, spare some thought for the work that went into making the object stand safely on it.