ratio is a fixed relationship of amounts or measurements, for example if the recommended mix for a plaster is 2 parts plaster to 1 part water the ratio can be written as 2:1. Sometimes this is expressed as a percentage i.e. 50% water to 100% plaster
A release agent is a temporary substance applied as a thin coating on a surface to prevent another material from sticking. For example plaster moulds need to be coated with a ‘parting wax’ before a resin cast can be made, similarly during lifecasting work a sitter’s face needs a protective coat of Vaseline before any mouldmaking material is applied. Some surfaces need to be sealed first if they are porous, as is the case with plaster needing a few coats of shellac before the parting wax. In other cases Vaseline (often useful as a general-purpose release agent) serves as both sealant and release, for example when making a silicone mould on a foam prototype
Vaseline petroleum jelly. A general-purpose barrier for most tasks (except when working with latex, polyester resin or absorption moulds). Can be thinned with white spirit
Soft soap or ‘mouldmaker’s soap’ A traditional release material, used for example in place of Vaseline when preparing for absorption casts because it can be easily washed away
FuseFX Royal Jel-E between silicone/silicone. Water-based meaning that it washes properly off. 2 coats applied, using hairdryer to set. Royal Jel-E can also be used to seal plaster cast for applying Chavant clay prosthetic modelling
.. or Smooth-on Ease Release 200 between silicone/silicone
R5 wax release agent spray £10.00 per 400ml (Tiranti)
PVA polyvinyl alcohol
As part of barrier between mould and polyester resin (usually after parting wax). 1litre £5.70 specialplasters, 250g £3.29 Tiranti.
Also termed ‘dimensional paint’. Can be found as ‘relief outliner’ or ‘relief paint’ for fabric decoration e.g Pebeo ‘Touch Deco’, or as outliner for glass painting ‘Cerne Relief’. Suitable in model-making for building up relief decoration on friezes, ornamental frames and furniture.
Those intended for fabric decoration have a ‘gummy’ consistency but come out of the tube very smoothly (easy to do steady lines and dots etc.) but on drying the thickness shrinks and the surface can remain a little tacky to the touch.
The tubes of ‘Cerne Relief’, also from Pebeo, for making containment lines for glass decoration, have much finer nozzles and the material keeps its thickness better. Dries with a plastic-like sheen. More expensive than other types. Pebeo ‘Gutta’ (a relief barrier medium for silk painting) also creates a raised pattern, but subtle.
Obtainable Cass Arts, Atlantis, some hobby shops Price (2013) fabric paints c. £2-3 a tube, glass painting outliner or gutta c. £3-4 a tube
A version which has much more body can be ‘home-made’ mixing Polycell Fine Surface Polyfilla with a very little water (i.e. 2 wets of the surface) until it is the consistency of thick cream, and piping using a plastic bottle with fine nozzle (£shops). Pipes well when fresh, takes 1+ hr to dry at 1-2mm thickness. Polycell FS also slightly flexible and sticks well even to plastic. But this will not keep long i.e. it should be mixed up as-and-when needed because it will separate and lump after a while.
‘Idenden Brushcote’ will also work very well for this, ‘pipes’ well, and it keeps its smooth consistency for much longer but it is expensive and it shrinks a little (see entry). Another thick liquid material that could work well is Rosco ‘Foamcoat’. Available 4D £12.75 per 500ml.
reservoir is the name given to a funnel or trough shape built as part of a mould around the pouring area to assist filling the mould with a liquid casting material. This ‘reservoir’ is much easier to pour into than a small hole and also the weight of liquid within it may help in forcing it into the mould
reticulated foam is a general name to describe the structure of any foam where the bubble walls disappear during formation so that what remains is a form of lattice created where the bubbles have intersected. The foam is therefore often described as an ‘open’ one. Reticulated foams are most commonly used as industrial filters (there will be a small piece in your vacuum cleaner) but model shops sell small sheets because the organic structure serves to simulate plants or trees in architectural or scenic models. Usually black, dark grey or beige but green (4D) can also be found. If needed in more bulk Pentonville Rubber Company in London (see ‘Suppliers’ page) can cut any width from a large block
rosin a.k.a colophony is a plant resin which is added to wax formulations to make them harder. At room temperature it is a hard solid but melts around 70-80C
sand and gravel for ‘scattering’ into glue to simulate model surfaces i.e. pebble beach, pebble-dash walls. Some good options available from pet shops. Smaller amounts (more expensive, but greater choice) from 4D modelshop or other model supply shops
sand casting casting traditionally with molten metal into negative shapes made by pressing a form in compact oiled sand. Jewellery makers still make use of this method. Petrobond oil-bonded sand price £3.30 per kg (mindsetsonline.co.uk, 2013). Special for sand-casting, fine reproduction of detail
sandpaper I would recommend Norton ‘Oakey Liberty Green’ especially for coarse P60 (B&Q) and yellow Mirka ‘Hiomant E’ P120 for general sanding. These are good quality sandpaper types that are guaranteed to last. The coarsest commonly available to buy is P60 grade but there is a P40 available from Buck and Ryan, London. For fine sanding J-Flex Abrasive Cloth e.g. P180 grit (Tiranti). This works equally well on either hard or soft surfaces
scalpel a sharp, fine, surgical knife usually comprising a metal handle and disposable blades. Those made by the Sheffield firm Swann-Morton are recommended (together with type ’10A’ blades), and generally found in good art or craft shops. These are better than common ‘craft’ knives because the blade is supported well in the handle and doesn’t bend or wobble like some of these do. The ’10A’ blade shape (a straight cutting edge with a gradual angle) is recommended as the best average shape (out of all the choices) for cutting both straight and curved lines. Curved blades are ineffective for model-making work!
Sculpey softener is a liquid which is available either to make the polymer clay a little stickier to assist bonding or for working into old Sculpey to bring back its plasticity (see ‘Super Sculpey’)
Sculptamold is a fibrous plaster mixture similar to papier mache. It is supplied as a pulpy powder to which water is added. Very useful either as coarse filler or (with less water) as thick modelling paste. Its main advantage is that it’s extremely lightweight, also has good adhesion on many surfaces, little shrinkage and is very hard when finally dry. Sets in just 30mins (due to its plaster content) but needs a long time (days) to fully dry. It helps if it has maximum air contact during this drying time. Obtainable Cass Arts, 4D Price e.g. 1.3kg bag £8.80 (4D)
seamless tiling the term for the digital technique of creating an area of perfectly joined pattern from a single ‘pattern tile’. Many pattern tiles can be found online, often (in Internet Explorer) by right-clicking on a webpage pattern and right-clicking ‘Save background as’
SG (‘specific gravity’) denotes the weight of a material per 1 cubic centimetre. Water has a specific gravity of 1, used as a benchmark because 1 cubic centimetre of water weighs 1 gram. The SG number gives the weight of 1 cubic centimetre of the material i.e. silicone rubbers usually have an SG around 1.3, so 1 cubic centimetre (or millilitre in other words) will weigh 1.3 grams. If a product includes its SG number on the labelling, the weight of any volume can be easily calculated
shelf life is the amount of time (usually recommended by the manufacturer) within which a material should be used before its properties start changing. In practice this is almost always longer than stated by the manufacturer but it will vary greatly according to how it is used and stored
Shellsol T is a ‘low odour mineral solvent’ for use with oil paints, but still requiring ‘adequate ventilation’ c. £6 per litre (apfitzpatrick.co.uk)
Shore A the officially recognised scale denoting rubber hardnesses, applicable to silicone rubber when fully cured. A Shore A value of 10 would signify a soft and stretchy rubber rather like gelatine sweets whereas 70 would suggest something more like tyre rubber. A general-purpose, medium hardness silicone would be between 20-25
Shore D denotes resin (but also hard rubber) hardnesses as a number between 1-100 and signifies the hardness when fully cured. For example shoe heel rubber is around Shore D 30 while hard-hat plastic is around 80. Biresin G26 polyurethane resin with a Shore D of 70 is therefore suitably hard
see ‘prosthetic silicones’ for the soft SFX types (I mean types of rubber .. not people!). See also page ‘Recycling silicone’, and other posts dealing with mouldmaking.
Silicone rubber is one of the staples of mouldmaking/casting, a synthetic rubber (wholly manufactured, unlike latex or alginate) used for making moulds and favoured for its durability, flexibility and excellent detail reproduction. RTV (room temperature vulcanization) silicone rubbers are supplied as liquid part and catalyst which, when mixed together in a specific ratio (usually anything from 2.5-10% catalyst to rubber by weight), will harden or ‘cure’ at normal room temperature in up to 24hrs. Most can either be poured once catalysed or thickened to make a spreadable paste. The flexibility of silicones is measured according to the ‘Shore A’ scale, somewhere between Shore A 20-30 being best for most general purposes. There is no ‘average’ pot-life (working time) since types and brands differ widely but it can be anything from a few minutes to a couple of hours.
Advantages Excellent flow properties with best detail reproduction; widely available, many suppliers; very good flexibility, tear strength; good separation from most surfaces without the need for release agents (except from silicone itself, glass, and highly porous prototypes); moulds are durable and long-lasting; easy application, though care needed (generally adequate pot life to spend time on the mould); accepts all casting materials; choice of pouring for block moulds or making thixotropic (gel-like) for skin moulds; good ‘memory’ i.e. when silicone is split the two halves it will ‘marry’ again well and form a good seal; low shrinkage (condensation cure silicones generally 1%, addition cure silicones generally 0.1%); many varieties available i.e. different hardnesses and tear strength, working times, cure times, chemical or heat resistance, library life; easy clean-up before curing with white spirit; can be coloured with up to 10% weight powder pigment (i.e. when using as casting material or when colouring different layers for skin build-up)
Disadvantages Normally long total cure (24hrs recommended); can be expensive at average £22 per kg, no cut-price versions and little reduction for buying in bulk (volume is even less because it’s sold by kg and average SG is around 1.25); not re-usable once cured (but can be recycled by granulating); limited shelf-life average 6mths-1yr (according to manufacturers); mixing needs attention (fairly accurate dosing of catalyst needed, especially thorough mixing in pot); sensitivity of addition cure silicones to chemical influences; will absorb some of the plasticizers from polymer clay prototypes during mouldmaking
Mixing and pouring or applying silicone Dose catalyst reasonably accurately (more accurate by weight, but use pipette by volume for amounts too small to read properly on scales); mix for at least 5mins, scraping sides and bottom of cup properly; containment walls to receive poured silicone must be ‘watertight’; small prototypes must be secure if material is lighter than silicone’s average 1.25 SG; pour down side of containment, level rising slowly inside or apply detail coat while silicone is most fluid; silicone can be poured in layers (makes no difference if layers set in between because it will fuse); mixing sticks should be clean, disposable bamboo chopsticks recommended for strength;
Conversion if mixing by volume instead of weight/- weigh (or calculate weight if SG is known) 100ml of silicone, divide by percentage of catalyst to find required weight of catalyst per 100ml, find SG of catalyst, divide this into weight of catalyst needed, to find number of ml of catalyst needed.
Caring for silicone moulds
Cleaning off all residues plus soaking/washing in warm soapy water after use. Covering to prevent dust attraction. 2hrs heating in oven (100C) to evaporate contaminents. Using release agents e.g. Vaseline just to protect mould even when not necessary.
Comparison of types, notes on them and prices 2013
Lukasil 429 silicone rubber £20.59 per 1.1kg, £95.30 per 5.5kg (specialplasters.co.uk) Light pink colour (rubber white, catalyst red) 10% catalyst by weight (12.8% by volume, so 100ml rubber needs 12.8ml catalyst). Shore A 20, coloured catalyst (makes thorough mixing much easier to judge), shelf life 6 months (according to manufacturer, but I often use after more than a year with no noticeable consequences), total cure 24hrs (can often be demoulded sooner). 0.5-1% thixo £6.60 per 100g (at 1% 100ml needs 1ml thixo). SG rubber 1.24, SG catalyst 1.00 September 2012 1ml thixo per 100g silicone was too much with new batch of 429. Even 0.5% thickened up more effectively than before. Both catalyst and thixo can be added by volume since both weigh near the same as water i.e. 1ml equaling 1g
Tiranti T28 silicone rubber £22.06 per 1kg, £93.98 per 5.25kg (Tiranti) A good average; relatively soft, tough but elastic, allowing some undercutting (Shore A 25). Very pale grey/white colour. 5% catalyst by weight (6.72% by volume, so 100ml rubber needs 6.72ml catalyst). SG 1.29, withstands up to 200 centigrade, shelf life 6 months (but see below), pot-life 100mins (less with thixo), cure 24hrs. 0.5-2% thixo £6.34 per 50g (1% works well if thoroughly mixed). Can be coloured by adding up to 10% weight powder pigment. ‘T5 fast catalyst’ now available (coloured) to reduce cure to 2-2.5hrs (mixed 5%) but also reduces pot-life to c. 15mins. Costs extra £6.46 per 50g, £12.94 per 250g July 2013 be aware that a 5kg can of T28 will contain just 3.875 litres of silicone, since the SG (weight) of T28 is 1.29 grams per ml (weight of can on its own is c. 410g. Concerning shelf life, I recently used a very old batch of T28 from 2010 (2.5-3yrs old) with no adverse effects (used with new catalyst and thixo).
Tiranti T40 fast-cure silicone rubber £63.90 per 2kg (only size available) Light pink, sticky paste. Addition (Platinum) cure. 2 parts mixed 1:1, with just a few minutes working time and ready to be demoulded in 15-20mins. Shore A 40, can be thinned with silicone fluid. Suitable on skin for life-casting if barrier cream is used (avoid mouth and eyes).
Addition cure silicones are easily inhibited e.g. by sulphur in some plasticine types, epoxy resin, polyester resin, shellac, superglue, condensation cure silicones, latex etc. See ‘addition cure silicones’ for full list. Mostly more expensive than condensation cure silicones, but mixing is easier (1:1 parts), generally tougher with less shrinkage (i.e. 0.1 as opposed to 1%)
Tiranti RTV101 hard silicone rubber £23.16 per 1kg, £103.63 per 5kg (Tiranti) Brick red, pourable. 3-5% catalyst by weight. Shore A 55. Tough, designed for centrifugal casting using low-melt metals (withstands up to 316C). Pot life c.1hr, cure 24hrs at 3%cat, 5-6hrs at 5%cat. Apparently small amount of water added to mix will speed curing even more (Tiranti booklet). There may be danger of damaging delicate castings in resin when trying to remove them from the hard rubber.
Since this hard type of silicone withstands oven temperatures, a polymer clay such as Super Sculpey can be pressed into the mould and baked in the oven still inside it. RTV101 has little flex though compared to softer silicones and it may be difficult to demould delicate forms (in all but metal) without breaking them. For polymer clay baking a softer silicone could be used because most silicones withstand a temperature up to around 200C.
Rhodorsil V1069 £21.12 per 1kg, £100.32 per 5.5kg (specialplasters.co.uk) Light green colour (rubber white, catalyst green). Not pourable, comes as ‘gel’. 10% catalyst by weight (1.00 SG so can also be measured in volume). Shore A 30, long library life. Working time 60mins, recommended cure time 16hrs (can be demoulded in less), shelf life 18 months.
Cheapest available silicone rubber?
At time of writing (7/2013) Tomps are offering their ‘Value Budget’ range of RTV silicones (Shore A 20,25 or 30) for £50.00 (£60.00 inc VAT) per 5.25kg. These are just for pouring, not for thickening. Delivery estimated at £8-9
Shortlist of suppliers (see ‘Suppliers’ page for details) Tiranti; specialplasters.co.uk; mouldlife; Bentley Chemicals: Tomps, 4D, South Western Industrial Plasters …
Notes in progress..
When buying silicone rubber for a job requiring a specific amount it is important to remember that it weighs more than 1g per 1ml which means that 5kg of silicone (it is usually packaged in kg) will give you less than 5litres in volume. For example Tiranti’s T29 weighs 1.29g per 1ml so 5kg needs to be divided by 1.29 to give volume .. which is only 3.875 litres! Take recommended cure times seriously i.e. many silicones will appear to have reached ‘touch hardness’ long before the recommended cure time. This does not necessarily mean that it is safe to demould without affecting their shape
What often happens with silicone rubber well past its use-by time is not that it fails to cure .. in fact it is the opposite. It may start setting very quickly, so quickly in fact that it has become unpourable almost before proper mixing has finished. If it does this it may still serve as a thixotropic paste (without the need for thixotropic additive) as long as it can be used quickly. But if it sets too quickly even for this, I suggest mixing it up anyway, letting it cure and then recycling by grinding it down (see page ‘Recycling silicone’) rather than throwing it away
Simoniz acrylic primer is a good all-purpose spray primer sold as car paint undercoat (i.e. in Halfords etc, also from 4D modelshop) which dries quickly and gives an even, matte surface with a good ‘tooth’ to it i.e. will often accept even watery acrylic washes unlike some other spray primers i.e. Plasticote which has a more impervious, silky surface
skin mould when the silicone rubber (or latex) part of the mould is built up as a reasonably thick layer on the surface of the prototype (as opposed to being poured on as a contained block), but which then has to be supported by a separate rigid jacket. Skin moulds are much more economical since much less silicone is used compared to making block moulds, but they take much longer to make
skirting board is the UK term (‘baseboard’ in the US) for the wooden board fixed along the bottom of an interior wall to hide the gap between the wall surface and the ends of floorboards. This usually has a shaped profile along the top edge
sledging is the traditional name for the plasterer’s technique of creating a shaped wall moulding directly onto the wall (usually as part of the cornice) by running a wooden profile shape along wet plaster. It is possible to do this on a smaller scale for models
slush-casting the method of filling a mould partially with a liquid casting material which, by hand-turning or mechanically rotating the mould, forms an even coating inside resulting in a hollow cast when set. This may need to be built up in repeated stages. Often referred to as ‘rotational casting’ though it may not involve complete rotation
Smiths Deadener is a special additive for Platsil Gel 10 prosthetic silicone (Polytek) which turns it into an even softer gel so that the prosthetic part behaves and moves even more like flesh. The resulting gel remains sticky so it needs to be ‘encapsulated’ by first coating the inside of the mould with a thin layer of regular Platsil Gel which will act like the skin of a water-balloon. Obtainable mouldlife.net Price £37.58 per 1kg
sodium alginate see alginic acid, alginate
Sodium persulphate Obtainable as a powder which makes a brass-etching solution when mixed with water. The usual recommended mix is 100g powder to 500ml water. 0.1mm brass can take a few hours to etch through. Precautions; rubber gloves advisable, good ventilation, solution will damage fabrics, spent solution must be taken to re-cycling rather than poured down the drain. Obtainable Maplin or discountelectronicsstore.co.uk (as ‘PCB etch powder’) Price e.g 100g £2.26,1kg £16 (see ‘Metal etching’)
soldering is the method of joining metal parts using another softer and easily meltable metal alloy as a ‘hot glue’. If successful the bond is quite strong, though nothing like ‘welding’ (because the alloy itself remains soft). Thin brass, copper or tinned wire are the easiest materials to solder. Other metals such as silver, steel or aluminium can be soldered but not as easily. A soldering iron is used to heat up the parts to be joined sufficiently so that the alloy will melt on contact with them, flow into the joint and set. In addition to the special alloy another substance, the ‘flux’, is needed to aid the bonding of the alloy to the metal parts. Common paperclips (or some other similar office supplies e.g. drawing pins) can also be easily soldered because they’re normally coated with brass or tin. See page ‘A quick guide to soldering’ in Methods section
Solder a soft metal alloy in wire form which melts forming a bond between two pieces of metal. The standard for brass soldering used to be 60%tin 40%lead, but nowadays lead-free solders are safer and more common. I would recommend using one without a built-in flux for this kind of soldering work. Other metals need other more expensive types of solder (e.g. Carrs No 179 for aluminium). Silver solder can be used between brass and steel. Solder wire is also useful as a very flexible wire for low-strength armatures. Obtainable B&Q; Maplins; 4D modelshop Price c.2metres £1-4
Test 22/6/2013 Silverline brand solder (60% tin, 40%lead) £1.80 per 20g works very well with brass rod (1mm) and paperclips (these solder well as a rule)
Flux an essential fluid (or sometimes in grease form) which will clean and prevent oxidation of the metal surfaces to be joined. This layer of oxidation will prevent the solder from bonding with the metal if it is allowed to form. The standard cheaper type is fine for brass, while more expensive for other metals (e.g. Carrs ‘Grey Label’ for aluminium c.£13) Obtainable B&Q; Maplins; 4D modelshop Price c. £2-£10 per 30ml (dependant on type)
SOLVENTS AND THINNERS
See Materials page ‘Solvents and thinners’ or individual entries here for: white spirit, naphtha, WD-40, lighter fluid, turpentine, Bartoline ‘Clean Spirit’, acetone, methylated spirits, toluene, dichloromethane, isopropyl alcohol, surgical spirit, Shellsol T, Zest-It
spraymount has become a generic word (like ‘polyfilla’) to refer to any spray-glue used when working with paper or card. Properly speaking ‘Spraymount’ is the name 3M gives to its repositionable spray-glue, whereas 3M’s ‘Photomount’ is stronger and immediately permanent.
There’s a progression in strength with the various 3M products from very light-tack ‘ReMount’ (green top); then ‘Spraymount’ (blue top) repositionable up to 12hrs if sprayed on one surface, 2hrs if sprayed on both; then ‘Photomount’ high-strength permanent PH neutral; then ‘Displaymount’ (mauve top) even stronger for heavier materials. Finally ‘Craftmount’ is the strongest.
Craftmount will even bond sheets of styrofoam (or polyurethane foam from Kapa-line boards) well if sprayed on both surfaces, left for half a minute and the sheets pressed firmly together. I didn’t notice any dissolving of the styrofoam last time I did it. This method has the advantage that, if the glued surface is subsequently carved or sanded through, the spray glue won’t resist as much as some other glues, though it will still be a little tacky.
Cans should be shaken well before use, even though there’s no ‘rattle’ ball inside. Be aware of the black mark put on the top ring of the can which surrounds the spray nozzle. The nozzle should point in this direction for best coverage apparently.
13/7/12 Pink £14.95 400ml (CSM shop). Blue £7.65 200ml (Atlantis)
Tip 5/2014 although this only occasionally occurs, it can happen that the spray nozzle gets clogged. Sometimes this is just build-up around the spraying hole which can be removed using a scalpel or pin. Sometimes though the clogging is internal which can’t be dealt with. 3M cans all use the same nozzle, as far as I’m aware, and refitting another nozzle should solve the problem. Before you throw an empty can away keep the nozzle in case you might need it!
Spraypaints or ‘aerosol’ paints deliver a fine, thin and even covering of paint most suitable on flat or large areas.. Various types, those labelled ‘acrylic’ are not water-based (with some exceptions e.g. Liquitex acrylic water-based spraypaint 400ml c.£8.00). Humbrol produces a range of spraypaints matching a selection of its tin colours. I’ve found the best, most reliable and versatile, and the most economical spraypaints for model-making or sculptural work to be the Montana range (see below)
Advantages of spraypaint even coverage without brushstrokes; quick to apply and usually quick-drying; can utilise ‘overlays’ for creating effects;
Disadvantages much of the paint is lost to the air; ventilation essential; extensive workplace protection and masking needed; build-up of vapour and paint dust; will dissolve styrene-based plastics such as styrofoam, or in regular foamboard
Montana Gold 400ml cans, currently (June2013) £3.80 inc VAT, Montana Black £3.60 inc. per can from Chrome&Black www.chromeandblack.com Can will cover 2m sq area. Matte (slightly satin finish on very smooth surfaces). Difference between ‘Black’ and ‘Gold’ mainly that ‘Black’ is thicker and higher pressure spray, meaning that ‘Gold’ can be better for detail spraying (thinner lines) if used for graffiti. For spraying model pieces lower-pressure sprays are more suitable. Another low-pressure type is the quick-drying MTN ’94’ range (also from Montana), similar price.
split skin mould or just ‘split-mould’ describes a silicone mould (either poured as a block or applied as a skin) in which the silicone is partially cut with a sharp knife in order to remove the prototype or subsequent casts. In this way moulds can be made even for fully 3D forms without the need for separate mould pieces. It makes use of the ability of silicone to ‘close’ the cut again if supported properly and usually results in a very clean or unnoticeable seam
Also known as ‘oiled manilla’, impregnated with linseed oil. Very thin, cuts cleanly, stays rigid, can be directly painted even with acrylics without too much warping. Strong PVA will suffice to glue it but it will also take superglue well. Stains well for wood simulation (can also be scraped with sandpaper for convincing woodgrain effect). There are two thicknesses commonly available, the thicker (c.375microns, i.e. 0.4mm) is better suited to model work. See page ‘Working with stencil card’ in the Materials/ constructing section
In the US it won’t be found as ‘stencil card’ or ‘oiled manilla’ but something similar (or maybe even the same) goes by the name ‘oil board’.
Obtainable 4D; Paperchase; Atlantis; Cass Arts; Flints and most good art shops. Price e.g 76x50cm sheet £3-4.50 (cheapest at Flints or UAL shops). Online cheapest from Wright’s of Lymm www.stonehouses.co.uk
07/2013 currently cheapest in London from UAL college shops £2.35 per standard sheet
Styrene is one of the most common plastics, available in thin sheet or strip form, usually white but sheets are available in basic colours. It can be easily ‘welded’ together using the solvent dichloromethane or with superglue. ‘Snap’ method of scoring/bending sometimes used in place of cutting. The strip form is most familiar as the packets of EverGreen brand strips (wide variety of thicknesses and profiles) in model shops.
Available in sheets (0.13mm to 3mm) or in strips. Bends easily (more so than foamed Pvc) but harder to cut. In sheet form white, black or basic colours (strip form usually only white).
Obtainable 4D modelshop (London) Price (2013) e.g 66x68cm sheet of 0.5mm white £2.15, packets of strips £4.15 (4D)
See ‘Shaping styrofoam’ in Materials/-shaping
Usually light blue, ‘extruded polystyrene’ insulation material. Carves and sands well and available in various thicknesses. Is affected by solvent paints/glues i.e. superglue, UHU and most spray paints will dissolve surface. Strong PVA, ‘UHU Por’ or water-based ‘gap filling’ glues can be used to glue, or carefully placed strips of double-sided tape (also ‘Craftmount’ spray, see entry for ‘Spraymount’). It is also common in scenic workshops to laminate using 2-part rigid polyurethane foam. There are also pink/orange, green and white versions which have different densities and fineness, white being the finest and most expensive
Obtainable 4D (different types and thicknesses), some builders suppliers, panelsystems.co.uk, hindleys.com Price (2012) e.g. sheet 25x600x1250mm £12.70 (4D)
I strongly recommend either Toolbox brand in tubes from Poundland (8 per pack .. 2014 there used to be an ‘Extra Strong’ but now they’ve taken that name away) or Loctite Precision (B&Q). It is far better to buy small amounts because it will begin changing after first use in contact with the air and may only last a couple of weeks, so at least with the small tubes there’s not so much wasted.
Methods sets better with slight moisture (usually from atmosphere, but can be assisted by running finger a little along surfaces to be joined first .. or breathing heavily on the work!); so-called ‘zip kickers’ can be used to accelerate/solidify, but small spray variety is distinctly unpleasant, and the bottle version is much cheaper in the long run. Alternatively superglue can be solidified instantly by sprinkling in baking soda!
Super Sculpey is a popular polymer clay, flesh-pink and slightly translucent, used extensively in the film industry for modelling character maquettes. It is very malleable, models with very little ‘push back’ and does not stick to fingers or modelling tools (sticks quite well to itself and fuses more when heated). It needs to be baked to harden and this can be done either in a domestic oven or (for small and temporary work) using a heat gun. Oven: 130 degrees C for c15 mins per 6mm of thickness. Heat gun: a good half minute on medium setting, held 5-8cm from surface, constant but slow movement (make tests because heat guns vary). Normally c. 2% shrinkage. Note heat gun baking is fine for small forms (i.e. 1:25 scale figure) especially if modelled in layers, baked in between. Heat gun will not penetrate enough for solid baking of larger forms, centre remains unbaked and will cause cracking long-term but this will not be an issue if making a temporary prototype for mouldmaking/casting.
Cracking caused by; stress, insufficient baking, uneven baking (esp. with thick forms), infirm internal support, air inside sculpt, baked form cooling down too quickly. Can be largely dealt with by modelling in layers and ensuring proper baking. Repairs fill with superglue, leave, patch in (dependant on further purpose) with new Sculpey or Milliput. If filling cracks with Sculpey and rebaking, don’t put back in oven, use heat gun. ‘Premo’ less prone to cracking.
Versatile as a ‘casting’ material if press-moulded into any type of mould, carefully removed, then baked hard. If used with heat-resistant rubber (or plaster) moulds, Sculpey can be hardened directly in the mould (in oven or using heat gun), then removed (in fact, most silicone rubbers will resist up to 200 degrees C).
Price (2013) £9-11 per lb average (Canonbury Arts best price at £8.95) also obtainable Tiranti (£9.37), 4D, most good art or hobby shops
For more details see Super Sculpey in the Materials /- modelling section.
Notes in progress..
Modelling methods inserting hard elements such as ball bearings for eyes or modelling elements such as tusks/teeth separately, baking then inserting; smoothing using white spirit, olive oil or rubbing alchol;
Baking methods 1hr at 225F, 1hr at 250F, 2-3hrs at 275F (turns dark caramel). Turn oven off and leave sculpt there until cool. Smaller increments for thicker sculptures
‘Premo Sculpey’ bakes at same temperature but recommended 30mins per 6mm of thickness. Price e.g. (2012) £2.08 per 56g (Tiranti), £12.49 per 454g www.craftcellar.co.uk 24 colours available
surface area for calculation see ‘volumes and surface areas’
surfactant a substance which breaks the surface tension of a liquid, for example as detergent does. Light spraying of a detergent such as diluted Windowlene in a mould prior to casting in plaster will help to prevent the formation of air bubbles on the mould surface
surgical spirit also known as ‘rubbing alcohol’ with ethanol (or ‘ethyl alcohol’) as its main constituent along with methanol (or ‘methyl alcohol’). Can also contain isopropyl alcohol ( versions containing mainly isopropyl alcohol usually called ‘Isopropyl rubbing alcohol’ ). Like methylated spirits it is often coloured and made ‘bitter’ to prevent drinking. It’s most used as a disinfectant and as a toughener for the skin. Some brands contain castor oil to counteract dryness
Uses traditionally used by guitarists and ‘hill walkers’ alike to prevent blisters by toughening the skin; as a cleaner/disinfectant for minor cuts, clinical equipment and surfaces and skin prior to injections
Safety data highly flammable; harmful if swallowed; good ventilation necessary to avoid inhalation dangers; irritating to skin, can cause burning sensation
Obtainable chemists e.g. £1.35 per 200ml Superdrug
System 3 a range of inexpensive acrylics from Daler Rowney. Although behaviour will differ according to each colour pigment (in terms of opacity or coverage etc.) I’ve found them to work well on plastic, taking readily on Pvc for example even if thinned a little. However this will not be durable enough for repeated handling unless the plastic is properly primed first i.e. with Simoniz car primer