ABS short for ‘acrylonitrile butadiene styrene’ a tougher styrene form, very common in manufactured items, usually found in model shops as dark-grey construction strips or girder structures. Not so available in large sheets.
absorption casting is a method of filling a porous plaster mould with a liquid, water-based material such as clay slip or latex. It is a traditional method, but still a standard one in pottery manufacture The plaster absorbs the water and the material forms a shell which becomes a hollow casting once the excess liquid material is tipped out. Care must be taken that the plaster mould remains porous, so Vaseline cannot be used as usual as mould release from the prototype. Mouldmaker’s soap or washing-up liquid are alternatives. Specially porous plaster needs to be used i.e. ‘pottery plaster’ and the moulds need to be bigger to take account of shrinkage if size is crucial.
Advantages Light, hollow castings and economical use of material, with no wastage; an even structure; possible solution for thin/concave forms; allows casting in ceramics; allows work on surface in ‘leather’ hard state; minimises problem with trapped air in castings; thickness and strength can be controlled, according to how long mould is left filled.
Disadvantages limited to rigid plaster moulds; up to 10% shrinkage dependent on material; danger of damage when de-moulding; needs to be watched re. topping up the mould while shell is forming; little flexibility re. undercutting unless multi-part mould is made.
acetate clear plastic sheet more commonly used (A4-A3 size) in the past for creating OHP (overhead projection) visuals or as clear film to protect artwork. Usually thin i.e. 0.13-0.25mm. Ideal for representing glass in architectural models. Best to fix with double-sided tape as using superglue will cause ‘fogging’. Useful to represent gauzes in models esp. if organza is smoothly spraymounted onto it. Acetate can also be printed on (if it has a special coating) to suggest painted gauzes. It can also be roughened (very fine sandpaper or even kitchen scourer) to make surface less shiny or a little more opaque and this surface will accept acrylic in some cases.
acetone is widely used as a solvent and cleaner; present in many paints (particularly spraypaints) and some glues; used for thinning polyester and epoxy resins, will clean up uncured polyester, polyurethane and epoxy; pure acetone will dissolve superglue but only before it hardens completely; will attack and dissolve forms of styrene plastic inc. styrofoam, polystyrene; good degreaser of surfaces such as metal prior to painting; can be used as a releasing agent for transferring a toner photocopy (not inkjet print) to another surface.
Safety data highly flammable; irritating to eyes; dries the skin quickly, prolonged contact will cause dryness and cracking, can cause damage to eyes and nasal passages; vapours may cause drowsiness and dizziness
Obtainable see entry in ‘Solvents and thinners’ in the Materials section for current prices and suppliers.
Fast-drying, water-based paint with acrylic polymer as a binder, most familiar as artist’s acrylics in tube form. Many other paints can be labelled ‘acrylic’ but may have different composition i.e. not necessarily water-based, for example newer types of acrylic spraypaint.
Advantages fast-drying, quick and clean over-painting possible; thinning and clean-up with water, no need for other solvents; can be applied to absorbent surfaces and will harden there properly without priming; retains some flexibility on drying and doesn’t crack; can be intermixed; dried acrylic on mixing palettes will soften under warm water for easy clean-up; does not yellow with time
Disadvantages dries slightly darker; dries too fast for wet-blending; wastage on palette; tube acrylic tends to dry with a silky surface
Bottle acrylic (DecoArt, Inscribe, FolkArt, Anita’s etc.) This type of acrylic paint, sold in plastic bottles, is much more ‘model friendly’ being thinner, generally more opaque and matte than standard tube acrylic. Obtainable many art or hobby shops. 4D (small selection), Tiranti (Anita’s) Ryman’s, The Works (Royal & Langnickel brand .. though many of these are far too glossy!) Price (2013) £0.99 -£1.99 for a 59ml bottle
Rosco scenic paints i.e. ‘Super Saturated’ range. Super-concentrated matt acrylic paint which will still provide full coverage even when heavily diluted, with good adhesion on many surfaces. Diluted 1:1 with water as standard i.e. so 1litre will make 2litres of regular paint. Designed even to adhere to metal and plastic (limited durability). Normally only available in 1litre amounts unless buying the ‘starter’ or ‘tester’ kit comprising 28g pots of the whole range for £66 (Flints) Obtainable 4D, Flints, Brodie&Middleton Price 1ltr £14-28, 250ml £4-8 (4D, 2013)
acrylic retarder is a colourless gel medium which slows down drying of acrylic paint making it much more ‘workable’ and transparent (if required) for ‘scumbling’ and glazing. Obtainable art shops. Price Winsor&Newton c.£8-10 per 237ml tub 2014 Winsor&Newton may have discontinued it’s gel retarder in favour of a liquid version.
Spectrum gel retarder £5.77 per 125ml, also Screenprint Gel £6.98 per 250ml (2013).
For home-made retarder using glycerin: http://www.paintingclinic.com/clinic/guestarticles/retarder.htm
addition cure or ‘platinum cure’ silicone rubbers cure by the addition of platinum and they make up a large proportion of the silicones in general use together with ‘condensation cure’ or tin curing silicones which are perhaps the more common of the two for regular mouldmaking purposes. Addition cure silicones are normally mixed in two equal parts, which is somewhat easier, but curing can be affected by contact with certain substances such as sulphur (in some forms of plasticine), soaps, amines, tin compounds, epoxy or polyester resin, shellac, superglue, condensation cure silicones, silicone-based release agents, latex (including latex gloves), garlic or onion vapours. They are not affected by Vaseline. They are also usually more expensive. Many need additional heat to achieve complete cure. For these reasons condensation cure silicones are a better option for the beginner making regular moulds . For regular mouldmaking purposes their main advantages are strength (against abrasion and tear), generally longer library life and shorter cure times. There may not be a choice when selecting a very soft silicone for prosthetic or puppet work since the majority are addition cure. See also the post ‘Flexible puppet hands’ April 19th 2012
additive casting is my own term (for want of a better one so far!) to describe the method of casting parts of a complex form in smaller, separate moulds which are then fitted in place in the main mould after which the rest of the cast is poured. This will work best using resin, especially polyurethane, since fresh resin will readily fuse with the parts already set. See the post ‘January mouldmaking exercises – ‘Two legs good ..’ January 29th 2012
Alginate is a flexible mouldmaking material used primarily in life casting. It is skin-friendly, fast-setting and reproduces skin detail amazingly, but very fragile (compared to silicone) and normally has to be used immediately to make just one casting in plaster. For more see ‘Quick view comparisons of mouldmaking materials’ in Materials section and the post ‘Casting polyurethane resin into alginate’ November 9th 2012. Alginate contains a gum, sodium alginate, which is derived from algae (brown seaweed); jacket support necessary since it will rarely hold its shape on its own.
Obtainable see ‘Quick view comparisons’ for current prices and suppliers. Mixed 1:1 alginate:water by volume (add water gradually, mixing in) sets in 2-3 mins (fast) or 6-8mins (slow type). Moulds are temporary, limited flex, shrink quickly and normally not used with resins. Fast mixing and application requires some practise! Excellent detail reproduction; less than half the price of silicone (i.e. 1kg will yield twice the volume of material)
5/11/2012 tests done using Industrialplasters.com slow set alginate (CSM college shop £10.80 per 550g). Can be mixed for pouring consistency by adding 2-times volume of water. 100ml (firmly tamped) of alginate was mixed with 200ml of (room temp) water until it was a thin ‘custard’ (this ratio made roughly 200ml of set mix, so alginate volume is doubled). Mixing was easy with medium-sized painting brush. Mould was demoulded after 15mins, released easily, accomodates undercuts but material is fragile (very like tofu). Good reproduction, some air bubbles. The mould surface was dried with a tissue and carefully vaselined. G26 PU resin mixed and poured. After 20mins resin set as normal and there were no indications that it had been affected by the moisture content. The Industrialplasters.com alginate can also be mixed as normal, equal volumes alginate and water for a spreadable, stronger mix.
alginic acid derived through an industrial process from brown seaweed. This is then converted into sodium alginate which is a food-safe gum widely used as a thickener or gelling agent in food or cosmetics. It is responsible for the impression-making properties of the alginate used as a mould material for dentistry and life-casting. Here it is combined with various filler materials.
alpha and beta Used to differentiate plasters, an ‘alpha’ plaster having high mechanical strength i.e. especially strong, fine, hard-setting and dense, whereas ‘beta’ plasters have a lower mechanical strength, because they are more porous. An alpha plaster therefore may be the ideal choice for fine castings or where structural strength is needed whereas beta plasters can be more easily carved and are essential in the case of absorption casting. The difference is a result of the way gypsum (which is the raw material of all plasters) is processed. Alpha plasters need much less water when mixing than beta plasters
Aluminium wire Because relatively soft, even thick aluminium wire can be bent easily making it ideal for sculptors’ armatures etc. Cuts easily. The best choice for bendable puppet armatures, although always test bending tolerance beforehand (2 twisted strands of 2mm wire make a good, longer lasting, but still bendable support). Can be found either in circular or square section, often sold by weight rather than length. Aluminium wire can be soldered together (requiring special flux and solder) but this can be problematic. For armatures hot melt gluing with wrapping of garden wire also works very well. Obtainable see ‘Quick view materials info’ under ‘metalwork’ in the ‘Materials’ section for current prices and suppliers.
armature an internal structure meant to support modelling clay while sculpting a form, most commonly in bendable aluminium wire. It also refers to the movable skeleton inserted inside a stop-motion puppet which is often engineered in steel with ball-and-socket joints. Armatures for modelling are not just there for physical support, but just as much as a guide indicating where to model. Sometimes a ‘back iron’ is needed to take weight off the armature itself when modelling a large figure.
ASA (acrylonitrile styrene acrylate) another common form of styrene plastic sold as a model-making material though not normally in sheet form, more familiar as pre-shaped (i.e. square, rod or half-round) strips and most often white.
balsa wood Fragile as constructional material, better suited in combination (i.e. as cladding over a stronger structure in Pvc or card) or as easy means of making wood shapes which are not structural. Rough sanding will create fibrous surface, wire brushing will increase this effect. Quite difficult to sand down ‘against’ the grain, much easier along it and slices easily. Stains well with regular wood stain (though spirit-based infiltrates much better) but it may be difficult to obtain a dark, rich colour. Obtainable see ‘Quick view materials info’ under ‘constructing’ in the Materials section for current prices and suppliers.
Thinnest sheet form 0.8mm, thinnest strip form 1.5×1.5mm (4D)
Bartoline ‘Clean Spirit’ marketed as a ‘water-based alternative’ to white spirit or turpentine, with a minimal solvent content (below 8%). Bartoline claims that it will clean both oil and water-based paints from brushes and can be used as a degreaser. It is apparently odourless, non-flammable and classed as non-toxic. I haven’t used this yet myself (it and other odourless versions of white spirit are comparatively new) but will update here as soon as I do. One thing I can say though is that if it is water-based it obviously can’t be used as a thinner .. it’s just for cleaning. Obtainable see ‘Solvents and thinners’ in the ‘Materials’ section for current prices and suppliers.
bicarbonate of soda or ‘baking soda’ can be dropped into superglue to make it set instantly. It fills and bulks out the glue making it more ‘gap-filling’. It is also a good way of building up ‘ice’ effects in a model.
binder the ingredient in paint responsible for three important things: holding the other ingredients (pigment, solvent etc.) together; the adhesion of the paint to a surface; the eventual hardening of the paint. For example in acrylic paints it’s an ‘acrylic polymer’, in artists’ oil paints it’s usually linseed oil. These binders can usually be found separately if one wants to make one’s own paint.
Examples of binders (prices from 2013)
Rosco SuperSaturated Neutral Base/- c.£12 per litre. Pure binder with no pigment, dries with some flexibility. Paverpol transparent/- £5.20 250ml, £7.80 500ml, £12.60 1litre (simplysculpt) gives a tougher paint, ideal for coating foams to strengthen them Spectrum Acrylic Copolymer Emulsion (available gloss or matt) 100% acrylic resin intended to extend acrylic colours. 250ml £7.26
LDM7410 Acrylic Polymer (specialplasters) useful general purpose polymer as paint binder, sealer for plaster/polymer casts and as glaze. More water resistant than Pva, recommended dilution 2:1 water to polymer. 1litre £6.36, 5litres £23.76
Gum arabic crystals 500g £7.95 from Wrights of Lymm
Bioresin claimed to be a non-toxic alternative to the more harmful resins such as polyester, derived from sunflower seeds. ‘1775 fast’ version £40 per kg average (Canonbury Arts, 2013). Non-toxic clear resin. Mix 1:1.5 resin:hardener by volume (Biothan/Biodur), pot-life c. 4mins. Vaseline inhibits setting.
brass most commonly available metal for small-scale work, in a variety of strips, tubes and sheets. Not as pliable as copper but much softer than steel. The most suitable for soldering. Can be cut (if thin) by scoring with a scalpel. Obtainable see ‘Quick view materials info’ under ‘metalwork’ in the ‘Materials’ section for current prices and suppliers.
brass shim or ‘sculptor’s shim’, ‘brass fencing’. Thin (c. 0.1mm) brass sheet used for making dividing walls in soft clay sculptures prior to mouldmaking. Scores and breaks fairly easily, can be soldered. An ideal material for etching with sodium persulphate. Obtainable Tiranti Price e.g. 16.5cm x 2.5metre roll £8.17 (2014)
Cabosil is ‘fumed silica’, a powder commonly used as a filler for resins but which can also be used to fill or toughen silicone rubber. Dust masks should always be worn when working with any form of crystalline silica to prevent breathing in!
The most readily available model-making material ‘on the street’, serving perfectly well for many things, but also has many limitations i.e. susceptible to warping, fragile when cut thin, does not bend well, does not last. Some i.e. recycled ‘greyboard’ can also be quite tough to cut. Perfect for ‘sketch’ or idea-development models (especially Finnboard). See individual entries, e.g. ‘Stencil card’, ‘Finnboard’
Mountboard/- good for basic walls but will warp if painted, will need strengthening and not suitable for slender detail (e.g. window struts) because it will break apart. Scale problem if used for fine work. Good for chamfering i.e. cutting a slanting edge as in passepartout frames. Other ‘mountboard-like’ cards, may be tough to cut. Greyboard/- or similar cheap recycled card. Harder to cut. Stencil card/- ‘oiled manila’ cuts cleanly, paints without too much warping, stains well. Finnboard/- very soft, perfect for quick mock-ups (off-white helps), can be soaked/curved. Made from 100% wood pulp.
catalyst a substance which brings about a chemical reaction, such as in the setting of silicones or resins. Often also referred to as the ‘hardener’. Sometimes this forms an equal volume to the other part, as with polyurethane resins. At other times only a very small percentage of catalyst is added to the body material, as is the case with polyester resins or many silicones
Chavant clay see ‘plasticine’
chicken wire so-called because it is commonly used for chicken coops, is more like wire netting than mesh. The wire is twisted together rather than welded at the intersections and galvanised to prevent rust, which helps glues or paints to grab the surface. 3 mesh sizes available (at B&Q ‘Blooma’ range) e.g. smallest 13mm. Roll 10m x 60cm £23.98 (2013)
chopped strand mat is a form of fibreglass matting in which short strands of glass are compacted together with a temporary binder, rather than woven in a regular lattice. There is a light version weighing 300g per sq metre and a heavier at 450g.
ciment fondu normally fine ‘high alumina’ casting cement, reproducing fine detail but reaching extreme hardness when fully set, suitable for outdoor sculpture. Good Tiranti booklet available from Edward Folkard Casting in Ciment Fondu. Often ‘detail coat’ first laid down with pure mix, then rest filled with sand or aggregate added. Must be left wrapped to cure for 24hrs to achieve full strength because it needs the water. Obtainable £5.86 per 2.5kg Colour grey/brown (Tiranti, 2013)
The term ‘clay’ is often used nowadays when talking about any soft modelling material regardless of composition, but here I am confining it to the ‘natural’ types of clay familiar to most, when fired, as pottery. There are separate entries for the others such as ‘polymer clay’, ‘plasticine’ or ‘modelling wax’
Natural clay e.g. ‘grey clay’ £11.88 per 25kg from Tiranti (2014). Very suitable (and inexpensive) for general modelling or embedding for mouldmaking, if only temporary. Grey ‘modelling’ clay recommended, because terracotta is often much stickier and can stain. If still ‘workable’ (i.e. still relatively moist) no barrier agent needed with silicone or Vinamold, but a dry or even ‘leather hard’ clay prototype would need greasing with Vaseline before silicone is applied because otherwise clay traces can be very difficult to remove from the cured mould. Hard clay can be revived by spraying with water.
In test (September 2012) damp grey clay released well from silicone and plaster (silicone not affected by moisture) and residues can be easily washed off. Best to cover in cling film while working to prevent drying out too quickly
cling film (‘plastic wrap’ or ‘Saran wrap’ in the US) is ultra-thin, stretchable plastic (PVC or polyethylene) sheet usually used to wrap food, mainly to prevent drying out. So-called because it partially sticks to itself making a tighter seal. The stronger ‘heavy duty’ type is useful for wrapping tightly around a mould to bind it together, instead of rubber bands. It is also effective in preventing natural clay from drying out.
There are other uses relevant here too! For example, when building up a silicone rubber skin on a prototype it is always better if the final surface is kept as smooth as possible and this can often be difficult to achieve once the silicone starts to get stickier. An easier method of smoothing, once the silicone has been roughly spread on, is to cover with a piece of cling film and work it about through the film, as shown below. Once the silicone has cured the cling film can be peeled off.
The same method is also effective when modelling with other materials, particularly when trying to achieve smooth and streamlined surfaces with very soft materials. Below I am using a wooden ball to transfer a concave shape to Super Sculpey but I didn’t want any of the woodgrain with it. The cling film is first stretched evenly over the Sculpey before the ball is pressed into it. The cling film also smoothes out the edges around the shape.
For interesting and evocative performance work using cling film look at the filmwork of Shelly Love
cold metal casting is the recognised term for describing the technique of filling resin with metal dust to give the surface of a casting an authentically metallic appearance. This is usually only a surface layer, firstly because that’s usually all that is needed and secondly because real metal powders are not cheap. Once the resin has fully cured the surface has to be ‘cut back’ or burnished (usually using steel wool) to bring out the metallic shine. The proportion of metal filler to resin in this surface coat needs to be quite high for it to burnish properly and look like the real thing. Recommended easy method is to mix a small amount of resin with a little over the same amount of metal powder by volume. The finished surface not only looks like real metal but behaves like it in some respects i.e. after a while it may need re-polishing because it tarnishes. Special agents can be used to enhance this, especially when creating a true verdigris patina on copper for example.
Although a reasonable effect can be achieved with polyurethane resin it is dulled because the resin is opaque. The full effect can be better achieved using transparent resins such as polyester or epoxy.
Technique and materials metal powder c.£10-£12 per 500g average (2013). Up to 4:1 metal powder to resin (by weight) can be mixed to make surfacing layer with either GP or clear casting resin, catalysed 2% (always add catalyst to resin in this case before mixing in metal). If proper ‘gel coat’ resin is used less metal can be added, c.2-3 parts metal by weight. Less than 2:1 is ineffective. Wait until rubber-hard, then fill rest with normal resin catalysed 2% for small forms (1% for larger). This can either be unfilled or if preferred, dark pigmented. Wait at least 72 hrs before ‘cutting back’ and burnishing. Note: Tiranti’s ‘rule of thumb’ is same volume of metal powder to resin plus ‘a little more’ metal powder, and they advise that if measuring by weight the content of metal powder to 1 part resin is; Aluminium 1.25, bronze 6-7, brass 5-6, copper 4-5, iron 6-7
colourant is the term used to refer to a concentrated pigment formulation designed to colour an existing paint or material without affecting its properties e.g. Polyvine Colourants, Mixol Universal Colourants (Leyland SDM, Wrights of Lymm)
condensation cure silicones also known as ‘tin cure’ silicones, are the most common silicone rubbers used in sculptural or prop-making work. Silicone rubbers are most often condensation cure unless otherwise stated. They are usually the cheapest and cure when mixed with a very small proportion of catalyst (2-10% by weight, dependant on type). The other type is known as ‘addition cure’ or ‘platinum cure’ and are mixed in two parts 1:1. See ‘addition cure’
conditioning a modelling material such as Super Sculpey means working it for a while between the fingers (or even using a device such as a pasta maker) until it has achieved its maximum malleability and uniform softness. This should be done with most modelling materials even if newly bought. But especially old Sculpey, even if has become hard and cracked, can be revived by rigorous kneeding and afterwards it will retain this softness for days, sometimes weeks. If Sculpey becomes particularly hard (meaning that it’s lost a significant amount of its plasticizer) a little Sculpey diluent should be added while conditioning.
cork in granulated form (fine, medium or coarse grades are available) as scenic, scatter material or added to paint to give it a texture.
cracking medium (also known as ‘crackle’ or ‘craquelure’ medium) is a special glycerine-type coating which, when applied between two layers of paint, causes cracking of the top layer. In actual fact, although the result looks like cracking, it takes place immediately while the top paint layer is still wet, because the glycerine layer prevents the paint from anchoring and as it dries it starts to contract, pulling itself apart. This will continue until both paint and glycerine layers are completely dry. Obtainable for current suppliers and prices go to the ‘Materials’ section, then ‘painting’ for the ‘Quick view materials info’ page.
Method the subject surface is first painted, usually with a dark colour which is left to dry thoroughly. The cracking medium is painted on as a second layer and when this is touch-dry another paint colour (usually lighter or contrasting) is applied as a third layer. The paint will start to ‘crack’ i.e. separate immediately. A lot depends on how the top paint layer is applied and what form of paint it is. The best results are obtained if the paint is laid on in quick, even sweeps without disturbing the cracking medium layer too much i.e. forcible stippling will not work, and without any over-painting (i.e. going over again). Using a brush will inevitably result in slight variations of paint thickness and the pattern of the cracking usually reflects this. Spraying is probably ideal if a thick enough paint can be sprayed. The ideal paint is not only fairly thick and opaque but should also not be too strong or sticky, because it needs to be ‘weak’ enough for separation to occur. Good results are obtained with the more liquid acrylics such as DecoArt Americana or DecoArt Crafters; cheap wall emulsion paint; or Reeves liquid tempera.
Above, if both cracking medium and topcoat are applied as thinly as possible the cracking effect can be kept at a small scale. Areas can also be lifted off by scratching before the topcoat has dried. These samples were made on stencil card using the natural card surface as a colour base instead of under-painting. This will work if the surface is a non-absorbent one.
Other sources 2013 Polyvine Crackle Glaze £6.35 per 500ml from Wrights; Craquelure 500ml basecoat £8.95, topcoat £8.95 from Wrights. LeFranc&Bourgeois 75ml cracking varnish £4.60 from Wrights
curing is the term used to describe the hardening of mixtures, such as resins or silicones, which set as the result of a chemical reaction rather than simply drying by evaporation of a solvent such as water or ‘setting’ due to the crosslinking of like molecules. The full length of time that this takes is referred to as the ‘cure time’.
cutting back is the term used to describe the action of working into the surface of a casting to expose what’s underneath. For example when metal filler is used in resin to give a metallic look the surface needs to be rubbed with steel wool to expose the metal particles and bring out the shine.