|Specifics: Photos of the equipment or the results.|
That shiny "chrome" plating on some Transformer toys is not applied by traditional electrical or dip plating, but by vacuum metallizing.
In this process, the part is placed in a chamber with most of the air pumped out. Metal vapor enters the chamber and condenses on the part to form a very thin and shiny metallic coating.
The most common metal used for this process is nearly-pure aluminum, which gives a "silvery" finish. To change its color to gold, red, or whatever is desired, a transparent, colored paint may be applied over the metallizing. A clear coat may be applied even if the metal's natural color is suitable, to protect the finish.
This metal coating, if made of a corrosion-prone metal like aluminum, may easily tarnish and grow dull if its protection wears off. Furthermore, it is very thin, and may flake, peel, or be worn away with prolonged play. When new, though, it looks totally rockin' cool awesome and rad.
Vacuum metallizing was especially common during the Beast Era, where it was a defining characteristic of the Transmetal sublines. The chrome on toys from this era will sometimes show an excessive amount of spiderwebbed cracking and flaking, far beyond that expected from normal wear. The problem was sporadic and unpredictable, not confined to any particular toy. Sometimes the cracking would show up almost as soon as the toy was opened; other times it did not appear until months or years later. Though the problem was fairly common, the majority of toys were not affected.
Toys produced and sold in the United States in recent years have used few or no plated parts, and the metallizing was omitted from toys in the Universe line which had originally featured it, such as the Transmetals. However, vacuum metallized parts have made a distinct comeback in TakaraTomy's Henkei! Henkei! line, where virtually every figure has at least something shiny, regardless of whether it makes sense or not.
- Vacuum Metallizing Plastic Parts - Paper on vacuum metallizing.