The process of electrotyping, or electroforming, was developed in the 1830s. There were two methods of manufacture; the method chosen depended on what was being made, as the technique was employed for many different kinds of objects and works of art - from small furniture trimmings or table top sculpture, to relief plaques, to life-size sculptures intended for outdoor display. Usually, smaller objects were made using a wax or plaster model (a positive), possibly with an iron armature already inserted for support. Large objects and sculpture were usually made in sections using a number of moulds (negatives).
The model or mould was placed in a copper-plating tank and copper was allowed to deposit itself by electro-deposition onto the surface of the positive object or negative mould, until it had built up to an adequate structural thickness.
In the case of the model option, the copper built up on the outer surface of the object, so the thicker the copper gets, the more the surface detail is lost. It was therefore not a good technique for large objects because you could not gain sufficient thickness of copper to retain much strength without losing visual quality. To counteract the potential weakness of this method, the wax-impregnated plaster model would often be left inside the object to give support.
In the case of a mould however, the copper built up from the outer surface inwards, so a greater thickness could be built up without blurring the visible surface of the sculpture, thus making it suitable for large objects where a greater thickness was required for structural strength. This process produces highly detailed surfaces, reproducing every mark of the sculptor's hand.
When a large object was made by the mould method, each copper section was then cleaned and joined together by brazing or soldering. The thickness of the copper that could be deposited meant that iron armatures were seldom required.
Electrotypes can be patinated in the same manner as bronzes, but now frequently have a natural, green patina which has developed on the copper over time. Either way, they are easily mistaken for bronzes at first glance.
Because the copper shell of electrotype sculptures may be very thin, they are particularly susceptible to corrosion if not cared for. Where constructed with a plaster core and possibly iron armature, any consequent ingress of moisture results in the expansion of these materials, leading to splits and eventual collapse. Repairs can be made by reproducing any large, missing or heavily damaged areas using copper sheet, and/or by reinforcing weak areas by introducing fibreglass resin. Like lead sculpture, such objects usually require the replacement of any iron armature with new stainless steel armatures and structural fixings.
As with bronze, protective coatings of wax or lacquer need to be applied to protect and maintain the delicate surface.