tamping is the term given to firmly tapping a mould when filling it with a casting material to aid the flow and dislodge any trapped air. It also applies to firmly tapping plaster to expel air and even out the consistency during mixing
tear strength refers, in the case of silicones and other flexible mouldmaking materials, to their resistance to tearing when flexed or stretched. It is not the same as the Shore A hardness, because softer silicones can sometimes have a greater tear strength
tempera paint i.e. Reeve’s tempera or ‘poster paint’, the cheapest colour paint around. Weak adhesion and pigment strength, but perfect for basecoating large areas. Available in 500ml bottles or cakes. Pva can be added. Obtainable most art shops Price (2012) c.£1.45 per 500ml (Atlantis)
Traditionally ‘tempera’ meant a paint which used a water-soluble binder such as egg yolk or size. When first developed ‘poster paint’ used glue size hence it was also referred to as tempera.
thixotropic agent or thickener. An additive to silicone rubbers or resins which thickens them from a liquid to a gel or paste form so that they can be spread onto vertical surfaces without slumping, or applied much more thickly in one go. Most often silicones or resins have their own specific thickener, bought separately, and these are not interchangeable
toluene is a solvent ingredient in many paints (particularly spraypaints) and glues. Thin, colourless liquid with a strong, sweet smell. Not miscible with water. A specialist material, expensive and not usually available from ‘general’ suppliers.
Uses as a solvent and thinner for many paints and glues; effective as solvent/thinner for prosthetic (addition cure) silicones and paints (i.e. SmoothOn ‘Psycho Paint); is used to melt/weld styrene parts in model kit making (but not to be confused with dichloromethane which does the same)
Safety data highly flammable; vapour (heavier than air) explosive when exposed to heat or sources of ignition; irritating to eyes, throat, lungs and skin; toxic to inhale or ingest
Obtainable 4D modelshop £17.99 per 1litre
tooling means the use of power or hand tools to modify a material once set i.e. trimming, sanding, sawing or drilling
trapped air avoidance
When moulding ‘high pour’ method for reducing air bubbles in mould material; thin layer then air compressor blast; or applying careful ‘impression coat’ with small brush.
When castingTwo different causes; air trapped underneath overhangs, bubbles on surface of cast (esp plaster) trapped by surface tension.
Using talc as mould release (when casting with resin). Doing an ‘impression coat’ in resin first. Breaking surface tension with a ‘sulfactant’ when casting in plaster.
http://www.youtube.com/watch?v=ZLww18JJ8hw
http://www.hirstarts.com/casting/advanced.html
try square is an indispensable tool for marking right-angles, shaped like an ‘L’ with a thick base and thinner upright. So-called ‘Engineer’s’ try squares are usually small (c. 5-15cm long) and made from machined steel
Tyvek ‘spun polyethylene’ sheet. Extremely durable, can be painted or even printed on, glued with Pva or superglue.
turpentine Whereas ‘white spirit’ is mineral or petroleum-based, turpentine on the other hand is vegetable-based, non-hydrocarbon, most often distilled from the resin of pine trees. It’s often referred to as an oil (e.g. Oxford English ‘a volatile pungent oil distilled from gum turpentine or pine wood, used in mixing paints and varnishes and in liniment’). Can be expensive and there is no cheap (i.e. B&Q or £shop) version. Strong smelling, considered harmful (more so than white spirit) and evaporates much more slowly. Because turpentine is plant-based many assume it must be healthier than other solvents but this is not the case!
Uses for thinning oil-based paints, for many superior to white spirit when working with artists’ oils; as ingredient in varnishes or wax polishes (i.e. beeswax dissolved in turpentine as furniture wax); also dissolves resins such as Dammar resin; medicinal use (see below)
Safety data flammable; harmful to lungs and respiratory system; irritating to skin; vapour irritating to eyes. With turpentine the confusion is understandable because it has been used in the past as a relief for joint or muscle pain, even toothache, by being rubbed on the skin. Also as inhalant to relieve congestion! Does thinning with turpentine give a smoother oil-based paint than thinning with white spirit? Some artists do say that tube oil paint thins more evenly using turpentine and that colours are brighter, but also that turpentine discolours in time.
Obtainable art materials suppliers e.g. Winsor & Newton Distilled Turpentine £7.99 per 250ml
UHU available cheaply in £shops such as Poundland. Can be forced to set faster by placing glued edge first in position then raising it a little to string the glue and putting it back in place. It will immediately feel firmer. UHU Por is a ‘foam-friendly’ version suitable for using on styrofoam or expanded polystyrene
undercutting for example, if a mould is being made around a head shape the neck part ‘undercuts’ the rest of the head (i.e. it’s much narrower) preventing removal of the head if the mould is made in just one piece
UV blocker or ‘UV stabilizer’ can be added to polyester resin to prevent yellowing due to the action of light. There is no blocker as yet available for polyurethane resin
varnish a clear and usually colourless medium which is painted or sprayed on and dries relatively resistant in order to protect the material or paint layer underneath.
Rustin’s white polish (shellac base, fast drying) may be good option (specialplasters 250ml £4.20). Polyvine acrylic varnishes (Leyland, Brodies, Flints). Brodie & Middleton Cellulose varnish (quick drying) 250ml £7.10 Craig&Rose Trade ‘Extra pale dead flat varnish’ oil-based £5.80 per 500ml from Wrights. Others/- FEV (shellac base), liquid shoe polish can have sealing function
Winsor&Newton matt acrylic varnish recommended as very matte.
Vaseline a common brand of petroleum jelly, useful as a general-purpose barrier or release agent. But not to be used in conjunction with either polyester resin or latex, or on a plaster mould intended for absorption casting
vermiculite a naturally occurring mineral used as soil additive for better drainage. Useful as scenic material crushed to suggest various sizes of gravel or scree. Vermiculite is flaky and easy to crush. Obtainable 4D (small bags), garden suppliers (large bags)
VINAMOLD
Vinamold is one brand name (Gelflex is another) for a meltable vinyl compound used for mouldmaking which turns liquid at around 140 C. It has a similar flexibility to silicone and is re-usable, though detail reproduction is not as good. Mould is ready as soon as it has cooled (c. 30-60mins dependant on size). Not for highly detailed or fine work (will cool too quickly around the prototype), limited mould life. Prototypes also need to be heat-resistant.
Vinamold hot-melt vinyl £6-12 per 1kg, £25-30 per 5kg (Tiranti, specialplasters.co.uk) Melts at c.150 C, poured at 140 C. 1kg equals 1 litre volume. Constant stirring needed. Can be applied to damp materials such as clay, but not meltable materials such as plasticine, plastic or foam. Re-usable many times if not over-cooked. Accepts casting in plaster, resins, and silicones. Slight ridges caused by rapid cooling of the poured Vinamold are often unavoidable.
Main advantages; quick, cheap and re-usable. Accidental overheating can release toxic and corrosive vapours (hydrogen chloride gas). Moulds not long-lasting, surface will deteriorate and mass will start to split. Problems with bubbles forming if prototype/base surface isn’t sealed (air underneath gets hot and expands). Modifying vinyl surface with heat gun, can be very carefully melted to go smoother. Special kettles available and recommended if vinyl is to be used a lot. These however are quite expensive. Saucepan on controllable hob sufficient if absolute care taken.
Also useful as quick intermediate prototype for making absorption moulds
vinyl paint e.g. Lefranc ‘Flasche’ matte vinyl paint (Cornelissen £8.50 125ml etc.) ‘extra-fine vinyl-based, intense streak-free coverage, velvety matte, opaque, can be diluted with water, good adherence, resistance to weather’
vinyl wallpaper a useful source of ‘ready-made’ textures. Large B&Q warehouses usually have a varied choice and open rolls for taking free samples. Will accept any kind of paint or stain but with different degrees of coverage i.e. vinyl pattern will partially resist very thin washes but this gives an interesting effect and will emphasize the texture. Soft paper backing
viscosity the ‘thickness’ of a liquid, commonly measured in cPs (centipoise). Water has a value of 1cP, blood around 10, whereas honey is in the region of 2,000-3,000 and peanut butter is around 250,000!. A low viscosity polyurethane resin such as Biresin G26 has a cPs of 70. Sometimes these values are written mPa.s (millipascal-seconds) but can be read as the same because 1 centipoise equals 1 millipascal-second.
Volumes and surface areas calculated
1ml (1000ml per litre) is 1 cubic centimeter in volume. Volume is calculated length x width x height. Circular surface area is Pi(3.14) x radius squared; sphere volume is 4/3 (133.3%) x Pi x radius cubed; surface area of sphere is 4 x Pi x radius squared.
warping occurs most often when a water-based medium, whether paint or filler, is applied to an absorbent surface such as wood or cardboard. It will not occur with spirit-based media. The solutions are .. to seal the absorbent surface first with a spray primer such as Simoniz Acrylic Primer; to paint in separate flat pieces, allow to warp and bend/straighten back as far as possible when dry before assembling piece; to paint on both sides to counteract the effect; to incorporate very strong straighteners (i.e. struts along the backs of walls); to paint surface colours or effects, or build textures, on thinner paper first, let this dry and then spraymount this surface onto piece
WAX
Modelling wax Excellent modelling properties but cannot be made durable. Normally used for maquettes or when mould/casting is intended. Normally filled i.e. contains fillers such as chalk or kaolin as part of the mix. Different hardnesses and plasticity available. Obtainable e.g. Tiranti Price (2013) Scopas White Modelling Wax (a ‘French style’ filled modelling wax) and Terracotta Wax £6.36 per 500g, £46.40 per 5kg.
See also page ‘Modelling wax’ in ‘Materials’ section
Cheaper than Sculpey; does not degrade or go harder with age; can be worked with hot tools or heat gun for more effects; is harder/more stable at room temperature, but softens very quickly with heat from fingers; sticks more readily to itself than polymer clays (esp. using heat). On the other hand it has less elasticity compared to polymer clay or even plasticine. Modelling waxes come in a variety of hardnesses for different requirements of modelling i.e. Terracotta Wax is excellent for quick and sketchy modelling whereas Scopas White stays firmer for fine detail and is more ‘elastic’. The two can also be mixed to achieve something in between.
For MMC course June 2013 Tiranti’s soft Terracotta Wax proved to be an ideal material for embedding prototypes and building containment walls during mouldmaking. Very malleable (as much as fresh natural clay) but firm enough; easy to peel or clean off set plaster or silicone; residues easy to remove from prototypes. But July 2013 used Terracotta Wax for dividing walls to form pieces of a mould jacket over a large silicone skin mould using Jesmonite. Whereas there had been no problem with plaster, wax would not easily peel away from the Jesmonite and had to be scraped off.
Wax suitable for ‘lost wax’ process is different because, although there are versions which can be directly modelled with, this type of wax has to melt completely to vacate the investment mould prior to substitution by molten metal. Generally this type of wax is therefore unfilled.
There is a modelling clay called ‘plastilin’ possibly manufactured by the German firm Becks (but not the same as the other German version of the same name invented by Franz Kolb) which is apparently wax-based rather than oil-based like the ‘plasticine’ which it resembles. Soft ‘ivory’ and harder grey available. Soft version does not ‘condition’ as soft as soft modelling wax types, sticks a little to fingers.
Price (2012) £5.10 per 1kg (CSM shop) or £5.10 ivory, £6.41 grey at Flints
wax gilt a suspension of real metal or fake metal (mica) particles in a soft, rubbing wax which is applied with the finger or a cloth to create a metallic surface effect. E.g. ‘Finger Gold’ or the ‘Treasure Gold’ range of metallic colours.
WEATHERING
Weathering wood For achieving a proper oxidised grey surface rather than faking with paint. Lye (strong alkaline) oven cleaner applied and left, must be neutralised with white vinegar. ‘Sweat and sour’ method/- Dissolve pad of fine steel wool in white vinegar (1-2 days), dilute with water and apply/leave. Can be further enhanced by leaving in sunlight. This method is also used for ‘ebonising’ wood using a more concentrated mix or soaking wood first in tea to provide more of the darkening tannin.
Using bleach …
welded wire mesh available in different gauges though most common has 12x12mm squares. Very useful for creating small trees. This is galvanized iron wire, welded firmly at each intersection. Because the surface is roughened PVA will ‘stick’ to it. Can be bent into shapes but, as a sheet, not as mouldable as impression mesh. Wire snippers needed to cut. Obtainable B&Q; Screwfix; Wickes; Wilko; good ironmongers such as Robert Dyas Price (2013) c.A1 size sheet (B&Q) c.£6.48, or roll (90cm x 6metres) £27.98
The process of galvanization (where a thin zinc coating is formed to prevent rust) makes the surface of the wire less smooth, with the advantage that even water-based glues such as Pva will adhere quite well to it.
See also ‘chicken wire’ for comparison
wetting refers either to the addition and mixing of a little solvent with a pigment (to prepare it prior to adding to a material or when making a paint) or, for example when working with fibreglass, thorough soaking of the matting with resin while applying layers
WD-40 Described as a ‘penetrating oil’ and ‘WD’ stands for ‘water displacement’. Flammable. Classed as harmful if swallowed or with repeated exposure (skin dryness, dizziness). Composition 70-80% ‘aliphatic petroleum distillate’ in other words ‘white spirit’ or ‘naphtha’; 15% mineral oil; 5% carbon dioxide gas as propellant. An oil diluted in naphtha, which then evaporates leaving the oil as protection/lubricant. Can soften leather, can damage some plastics over time.
Uses as a lubricant; as protection for metal against corrosion and also rust remover (or loosener of rusted parts); displaces moisture. Also often used as degreaser and cleaner tackling grease, some adhesives, even chewing-gum.
Safety data Highly flammable. Classed as harmful if swallowed or with repeated exposure (causing dizziness, skin dryness)
Obtainable household, car, ironmongers, DIY stores or supermarkets. Price (2013) e.g. Tesco £4.00 per 100ml; Halfords £5.99 per 600ml spray
white spirit UK name for cleaning solvent/paint thinner derived from petroleum (naphtha hydrotreated) known as ‘mineral spirits’ or ‘Stoddard solvent’ in the US and also often referred to as ‘turpentine substitute’. Not miscible with water. ‘Low odour’ white spirit is basically the same but with some of the ‘aromatic compounds’ removed
Uses as cleaner or thinner for most oil-based paints, including artists’ oil paints; used industrially as a degreaser especially for removing oils, greases from metal; will clean up uncured silicone rubber, can even be added to the mix to increase volume temporarily and can be added to Platsil Gel silicones to make a silicone paint; will dissolve coloured pencil and pastels to create washes or tints; when used as a carrier for pigment when staining wood, will penetrate better; good thinner for Humbrol enamels
Safety data Flammable liquid and vapour; harmful if swallowed; vapours may cause drowsiness and dizziness; repeated skin contact may cause dryness and cracking. Inspite of what the strong smell may suggest, white spirit is classed mainly as an ‘irritant’ and is considered harmful only in situations of extreme exposure i.e. if swallowed, inhaled progressively or soaking the skin for a long period
Obtainable all decorator’s, ironmongers or DIY stores. Price (2013) e.g. B&Q £1.68 per 750ml, £3.58 per 2litres. Bartoline Premium Low Odour White Spirit £3.98 per 750ml.
WIRE
Aluminium wire is the best option for large forms (i.e. large trees), easy to cut and bend and available in a variety of thicknesses. For smaller forms (i.e. small-scale figures) plastic-coated garden wire is recommended, twisted for strength Obtainable (aluminium) 4D modelshop; Tiranti (larger gauges); Scientific Wire Company www.scientificwire.com Price (2013) e.g. 3mm (1/8inch) square section x 37metres (1kg) at Tiranti £15.08 or 3.2mm x 1000mm single strip £1.36 (4D). Garden wire B&Q ‘Twist tie’; other DIY or £shops c. £1-2 per roll
wood stain properly formulated wood stains are most appropriate for changing the colour of model wood because they are designed to soak in and enhance (rather than mask) the natural grain. Generally spirit-based wood stains work better because they infiltrate more, do not warp the wood as they dry and do not ‘raise’ the grain like water does. These are expensive though, at up to £8 for a 250ml tin. Drawing inks, pure watercolour, liquid shoe polish, or pigment dissolved in white spirit are all reasonably good alternatives. Good watercolour paint can stain well and will not warp thin wood if applied sparingly. Look at Ronseal for fair-priced stains (for cheapest look at 50g Polyvine oil colourants at Leyland, or Wrights of Lymm £1.40)
Methods making test samples essential first; wetting wood first if using water-based; avoiding glue spots on surface while assembling; if using spirit-based careful re. dissolving glue underneath if double-sided tape has been used; many wood stains also have a sealer/varnish function.
Van Dyke crystals are also traditionally used for staining
Zest-It products, as alternative to white spirit or turpentine ..
davidneat 