Part Three – Materials
Brief notes on each of the materials listed in the course notes are below.
Pieces of paper mixed with glue or flour to form decorative objects or models. Most types of paper can be used for this method. My first thought was of sticking strips of paper to a balloon at school. The paper is allowed to dry on the balloon, the balloon is then popped and the dried paper takes the shape of the balloon.
Paper strips can also be used to mould the inside of an object.
A variation of this method could be using paper pulp. This can be easily prepared by using a blender to mince newspaper in to a pulp. This very soft mixture could then be pushed in to a mould to make a cast of the interior surface.
Conventionally used to cover interior walls plaster can be useful in casting objects as it begins as a liquid and then sets in to a hard object. This allows the plaster to work its way in to the intricate surface of an object and retain lots of detail from a mould.
This is an easy material to prepare as the plaster powder only needs to be mixed with water. Adding more water allows the liquid plaster to be poured in to more intricate mould but will take longer to set. This also makes the plaster produced more brittle.
Plaster powder contains gypsum and additional additives. When water is added it allows the molecules in the powder to move freely, these molecules then rearrange to form a crystalline structure. This happens relatively quickly, often in minutes, and allows the plaster to hold a shape well. The plaster still needs to dry out to hold any impressions made in it permanently.
Plaster of Paris’s name is derived from the large gypsum deposits found at Montmartre, Paris. Gypsum crystals from this deposit are heated until a dry powder is formed. This is then rehydrated by adding water to from a paste that can be used to cast and mould.
Plaster of Paris is also available on rolls of bandage, similar to those used in medical settings. These can be used to build up layers on the outside of an object.
Both plaster and plaster of Paris need some careful handling when in use. Adding water to plaster powder creates an exothermic reaction; that is it generates heat. In some cases this can be enough to burn skin. These items should not be held when setting and gloves should be used at all times.
Latex is not the sap of the rubber tree but taken from ducts just under the surface of the trees bark. Trees are ‘tapped’, or cut, to allow the latex to flow out of the tree and is collected in cups. On contact with the air the latex begins to dry out and will form lumps in the collecting cups.
To form rubber from latex it is heated to breakdown the proteins it contains and is then re-hardened. Latex is not heated but additional stabilisers are added to the concentrate retrieved from the trees.
Liquid latex is formed from latex, water and ammonia. Thin layers can be built up on an object to form a mould. Talc should be applied to the object being cast to allow the latex to be easily removed when dry. 8-10 layers are required to give a good cast.
Latex allergies are common so should be investigated before starting to work with this material if suspected, also there is a high ammonia content in liquid latex products and as such they should be used in a well ventilated area.
I do not like the smell or feel of this material so will not be using liquid latex in any of my samples.
Clay is a soft loose material that contains grains of less than 4µm. These grains are formed from the erosion and weathering of rocks containing feldspar.
Minerals in the clay have tetrahedral or octahedral structures, these pack tightly together in layer to bond the material well .
There are many types of clay, differing only in what material is used to make up the ‘grains’.
Pottery clay can be used to cast or mould but will require firing to keep the shape created in it indefinitely. Terracotta and Stoneware are examples but firing temperatures and clay mineral composition can change the characteristics of the finished item.
Firing clay may not be an option available to all but there are some domestic equivalents that can be used. FIMO is a synthetic polymer clay produced by Staedtler. It can be used in a similar way to standard clay. Casting and moulding can be achieved with this material and once completed the FIMO can be heat set in a conventional, domestic oven (30 minutes, 110⁰C).
Silver and metal clays are available. These clays contain metal particles and binders. They can be fired at home but require direct heat such as a gas stove top or a blowtorch so would need to be used safely. Due to the metallic components metal clays are very expensive, gram per gram, when compared to conventional clay.
Air-drying clay requires no extra equipment to set finished pieces. It is made from paper, resin and glue and will dry in open air over several days. It can be rolled and manipulated like clay and easily pressed in to moulds or on to surfaces. It can be revived by spraying lightly with water if it is a little dry when removed from the foil packet it is stored in. However once it is completely dry it cannot be reworked.
Non-toxic, lightweight polyesters, sold under trade names such as Thermomorph and Instamorph.
These polyesters are supplied as, in most cases, white pellets. These pellets can be melted at relatively low temperatures, around 66⁰C (150⁰F), into a colourless lump. This can then be sculpted by hand, moulded around objects or pressed in to its surface.
Once set this material returns to white.
This is relatively expensive but could be useful if a material needed to be pressed in to a mould as it is not liquid and can be easily handled.
A mixture of paste (Cement and water) and rocks or aggregates.
The cement and water paste coats the surface of the rocks or aggregate and once the water used in the paste has evaporated it holds the whole mixture together as concrete. There are many different recipes for making concrete but it is true of all of them that there must be enough water to hydrate the cement sufficiently and also enough paste to cover the aggregates sufficiently. Otherwise the concrete mixture will not have enough strength once it has dried.
Concrete may take years to dry but it will increase in strength over time.
Depending on how the concrete is mixed and applied to a cast or mould it is possible to make a very smooth or a very rough surface.
A variation on concrete where the cement and water is retained in the mixture but the aggregates or rocks are replaced with paper. The principal is still the same, the cement/water mixture coats the paper and when dried encases it to form a strong solid.
Sand or earth can be added to a papercrete mixture to add strength. This can then be formed in to bricks and buildings constructed.
This is still a fairly new and experimental method and no standard Papercrete mixture has so far been documented.
Sticky, flammable, organic substance, insoluble in water and often exuded by trees such as fir or pine. This is a definition of an organic resin. To cast or mould, a synthetic equivalent would be used.
Most common resins are Epoxy or Crystal Resin. These require mixing two parts in the correct ratio, usually liquid resin and a hardener.
Resin releases easily from silicone moulds, less so on plastic or those with too many corners.
Art Felt paper is designed to only dissolve completely in boiling water. This characteristic can be exploited to make casts of object surfaces. The paper can be torn in to small pieces and a brush and cold water used to slightly dampen the paper and push it in to the surface of an object. The paper will then dry out and can be removed from the object.
General Health and Safety
Each material has its own methods of use that should be followed however there are some general Health and Safety rules that it would be sensible to follow.
Always work in a well ventilated and well-lit area.
Gloves, safety glasses and at least an apron should be worn when using the materials listed above.
Wear a dust mask if powder is being weighted or measured out.
When heating any materials do not over heat them, ignition or breakdown of materials to harmful gasses is very possible.
If working alone, keep some method of communication, such as a mobile phone, close by in case of emergency.