Nothing betrays the hand of a poor prop builder quicker than something that is supposed to be gold, brass, silver or steel, but is obviously just a piece of wood or plastic covered with gold or silver spraypaint. No matter how good the shape, surface or decoration underneath might be, an unconvincing metal finish will ruin any prop instantly. On the other hand, a convincing metallic surface can often redeem lumpy and otherwise unfortunate props.
In order to understand why just reaching for the Krylon can doesn't turn a plastic goblet into pure silver, you first have to see the difference between real metal and paint. Oddly enough, many people just accept the label "Metallic Gold" at face value and never look at the finished product. Find a plain gold-spraypainted object (there's bound to be a few of them around the shop) and a piece of real brassware; set 'em up side-by side and step back for a look. The spraypainted object will be evenly coloured, smooth and satiny-looking and have a rather soft appearance, as though you could squeeze it. The shadows and highlights will be vague and soft. The brass object, however, will be darker in some areas and brighter in others, with dark reflections and bright, intense highlights. You can tell it's hard to the touch just by the way the light shines off it.
And that's the key difference: the way the light reflects off the surface. A metallic paint is made of tiny flakes of metal (usually aluminium or brass) floating in a clear binder. It's the light reflecting from all those bits of metal that makes us see the "metal finish". But though the microscopic flakes are real metal, they don't line up evenly, so they bounce the light around rather than reflecting it directly back at us like a mirror. This is why metallic painted surfaces always have that soft, flat look. The finer the metal flakes, and the clearer the binder, the more reflective the surface will be, but no metal paint will ever achieve the optical sharpness of the real thing.
Now, solid metal surfaces don't always reflect perfectly either: dirty, tarnished or corroded surfaces reflect much more like paint than like mirrors. This means that metallic paints can be useful, but only for metal that is heavily broken-down. For clean, respectable metalwork like silverware, gold crowns, etc., we need to start with a metal finish that is not broken up into tiny flakes.
The most direct approach, and surprisingly the one most often overlooked, is just to use solid metal in the first place. Gold is out of the question for most of us, but copper, brass, steel, aluminium, or silver or nickle plate are all affordable and workable. Instead of spraypainting those plastic goblets, buy cheap silver or brass ones. Instead of cutting up plastic icecream tubs to make crowns, start with brass flowerpots. Even having buttons, jewellery and other small parts cast in brass or silver is often surprisingly affordable. Aluminium and mild steel can be polished up to a very bright shine and simple hammering, soldering and riveting is often all the metalworking skills required.
The next best thing to a solid metal object is one that is covered with a layer of real metal. This can be either metal foil or metal leaf. The difference is mostly thickness: foil can be fairly thick, while leaf is only a few molecules thick. Foil is cheaper and easier to apply, but leaf gives a richer, less artificial finish, and will not obscure even the finest details.
Real gold leaf is very expensive, but "Japanese" or "Italian Gold Leaf", both artificial, are certainly good enough for stage use. Real silver leaf costs considerably more than aluminium leaf, and doesn't look that much different. Foil can be ordinary kitchen aluminium foil (the thicker "heavy duty" type is good for weapons and other larger props), coloured giftwrap or florist's foil, either smooth or textured. I've even used gold foil from baked potatoes. Paper-backed foil isn't usually much good, as it will not bend around curved shapes well. Mirrored mylar is astoundingly reflective, but again it just can't be made to curve onto complex shapes.
One of my new favourites is muffler tape. This is thick, self-adhesive, aluminium foil tape used for sealing mufflers and other hot metal surfaces. Because it has a good, sturdy adhesive on it, it's quick and easy to apply. Not as durable as contact-cemented foil, but permanent enough for most uses, and perfect for precise applications. The narrow width (only about 2" wide) is its biggest drawback.
Regardless what method you've used to metalize the prop, it will still need some more work to make it believable, as a clean, unbroken surface of leaf, foil or especially metallic paint always looks flat, shapeless and hard to distinguish. Even a prop that is meant to look new will need a small amount of breakdown.
As with any prop breakdown, the choice of techniques used for metal surfaces depends on the reality of the object you're trying to create. Some metals, like gold, hardly tarnish or discolour at all, even under the worst conditions, while iron, bronze and others have very characteristic reactions to weather and wear. A metal statue that's been kept indoors and cared for will still be glossy and shiny, while the same object in a park will be dirty, corroded and often show very little "metallic" surface at all.
For light or moderate breakdown, a wash of FEV, dilute scenic paint or tinted glaze is all that's required. Allow the colour to settle into crevices and hollows and wipe it off the highlights. If decoration is still getting lost, it may be necessary to paint in shadows to bring out contours and shapes. Raw umber or a cool brown are good breakdown colours for iron, brass and silver, while a warmer brown will be necessary for gold. Grey or bluish-black will give a better effect for steel or chrome. Remember to keep the breakdown wash as transparent as possible, to avoid killing the metallic effect you've created.
One of my favourite foil breakdown materials is black Varathane spray paint, which is slow-drying, translucent and very durable. A spray-on/wipe-off quickie is often all that's needed for weapons, silverware and other foiled surfaces.
It's important to remember that metal objects which have been exposed to the elements will show very little of the glint and shine of new metal. This is where metallic paint is most useful. A bronze statue, for instance, may have only the slightest metallic copper highlights over a brown and green base. Old, rusted iron really has no metal finish at all - it's all texture and colour.
Metallic paints consist of fine metal "bronzing" powder suspended in a clear base. Often the problem with commercially-made metal paints is that they contain as little metal powder as possible -- it's the expensive part. If you mix your own metallic paints, you can control the amount of bronzing powder, and therefore the brightness. Clear scenic glaze makes a perfectly good binder, although it will cause the bronzing powder to oxidize and change colour quite quickly, so don't mix up more than you can use in a few hours. A favourite trick for old, weathered metal (iron, bronze, copper, etc) is to mix bronzing powder - gold, silver or copper - directly into scene paint. It will rise to the surface as the paint dries, giving a subtle metallic sheen which often needs no further breakdown.
Here are some suggested techniques for simulating different metals. Remember that there are always several ways to achieve any finished effect.
Bronze (clean) (1) Aluminium foil coloured with dark, warm brown FEV, partially wiped off highlights. (2) Brown paint with copper powder mixed in, coppery-gold painted highlights
Bronze (weathered) Burnt umber, washed with phthalo green (green glue also gives a nice effect) for verdigris. Highlights in either light coppery-gold or pale, chalky green, depending on the degree of wear.
Gold (1)Gold-coloured foil or gold leaf, with warm brown or golden brown FEV in shadows. Silver or aluminium foiled objects can be turned to gold w/ an overall wash of warm golden FEV. (2) Very large objects can have gold foil applied to the highlights only, and the remaining areas painted with gold paint. This is more efficient and still quite convincing.
Brass Gold-coloured foil (leaf is too warm) with a wash of neutral brown FEV or glaze. Brass should appear slightly cooler than gold.
Silver Aluminium foil w/ neutral brown or black FEV or glaze breakdown. To look opulent and convincing on stage, silver should look smooth and polished, not glittery and harsh.
Steel Same as silver with cooler brown or bluish black breakdown.
Iron Black paint with aluminium powder mixed in, with silver paint highlights; broken down with brown glaze or FEV; spattering or wash of red oxide scenic paint for rust.
Copper (1) Copper foil or leaf, with cool brown FEV or glaze breakdown. (2) Brown-tinted copper paint base w/ bright copper paint highlights.
Chrome The hardest to fake. Aluminium foil with minimal breakdown, mylar highlights where possible. The best solution is just to have the object chrome-plated.
Often the problem with unconvincing metallic surfaces is not the metal finish itself but what's under it. Upholstery usually gimp isn't anything like decorative cast metal, and painting it silver just makes that more obvious. A piece plain of plywood just doesn't look like a halberd, even when it's covered in foil.
First, if you're turning a wood or plywood object into metal, you must seal, sand and fill the surface until all trace of woodgrain is eliminated. Metal effects will just emphasize the characteristics of the wood underneath. At least two or three coats of shellac will be necessary, sanded smooth between each. A lacquer-based sanding sealer like Pratt & Lambert will give you a good, smooth surface in one or two coats. A coating of a surfacing product like Foam-Coat, or a layer of tissue and white glue will also block out any trace of the underlying grain.
Remember that metal is a hard material, and metallic finishes just won't be convincing on soft surfaces such as fabric, gimp, rope or foam. The first step must be to seal and stiffen soft parts of the prop with polyester or epoxy resin, white glue, paint, Sculpt-Or-Coat or some other product that dries to a hard surface. Both metal foil and leaf will only work on a surface that's firm enough to let you burnish them properly.