The term FEV comes from "French Enamel Varnish", which was the name given by cabinetmakers to the mixture of shellac, alcohol and dye used for traditional French polishing. The term still refers to the same mixture, though we often use it for quite different purposes. Because it is tinted with dye rather than paint, FEV gives a completely transparent glaze with great depth of colour, which can be used in varying degrees of intensity to completely change the colour of an object (such as a yellow glaze over silver to produce gold) or to give a subtle patina to the surface to suggest age or wear. The advantages of FEV over other glazes are that it is transparent, durable, very liquid (runs easily into crevices and details) and dries very quickly.
In recent years FEV has gotten a bad reputation, and some prop builders still treat it as a kind of "liquid death" that must never be touched. Certainly the mixture that was blithely splashed around in the past was an amazingly toxic brew, but contemporary shops have learned to substitute less toxic materials to achieve the same effect.
Traditionally, FEV was coloured with aniline dyes, which give very intense hues. Concerns over the safety of exposure to aniline dyes, especially in powdered form, have led to the substitution of other dyes that are less toxic or less easily absorbed into the body. Some shops use food-grade powdered dyes, such as Orosol, but in most shops the easiest solution has been to switch to alcohol-based leather dyes such as Fiebing's. They come in very concentrated colours, including a good range of earth tones, and being already in liquid form, are much safer to work with than the easily inhaled powders. Note that Tintex, Dylon and other common fabric dyes will not work in FEV, as they are not soluble in alcohol.
The other toxic part of the old FEV was the solvent, which was traditionally "meths", or Methyl Hydrate. Methyl alcohol is very toxic, and very easily absorbed into the body by inhalation, skin absorption or through the eyes. There are other alcohols, however, which are much less harmful and which work as well. The safest is probably pure ethyl (grain) alcohol, but government regulations in most countries make it difficult or expensive to obtain. Most shops today make FEV with either "denatured" alcohol, which is ethyl alcohol adulterated with just enough methyl to make it toxic to drink (usually 10 to 15%), or with isopropyl alcohol, more commonly sold as "rubbing alcohol". Isopropanol is more toxic that ethanol, though still far safer than methyl alcohol. The other problem with isopropyl is obtaining it in pure form - what is sold in drug stores is diluted with water, often as much as 40%. The water reacts with the shellac and prevents it from drying properly. However, 99% pure isopropyl does seem to be more commonly available in drugstores these days, and pure isopropyl or denatured alcohol can always be bought in bulk from industrial chemical suppliers. Also check with local distillers in your area - many also produce industrial alcohols, and usually charge about a fifth of the price you pay from a laboratory supply house.
Some prop builders use different proportions, but the mixture I use for FEV is about 1:10 shellac to alcohol, with dye then added to achieve the necessary depth of colour. This is enough shellac to act as a binder for the dye, but not enough to produce a noticeable shine on the surface. If you want the FEV to add gloss as well as colour, increase the proportion of shellac as needed.
Note that shellac comes in two forms: white and the less-refined orange
or brown. White is usually preferable for FEV, as it does not affect the
colour. Liquid shellac contains methyl alcohol, so it does increase the
toxicity of the mixture. As an alternative, you can buy dry shellac flakes
(available from specialty wood finishing suppliers) and dissolve them yourself
in a safer form of alcohol.