Foil (metal)
A foil is a very thin sheet of metal, usually made by hammering or rolling. Foils are most easily made with malleable metals, such as aluminium, copper, tin, and gold. Foils usually bend under their own weight and can be torn easily. The more malleable a metal, the thinner foil can be made with it. For example, aluminium foil is usually about 1/1000 inch (0.03 mm), whereas gold (more malleable than aluminium) can be made into foil only a few atoms thick, called gold leaf. Extremely thin foil is called metal leaf. Leaf tears very easily and must be picked up with special brushes.
Diamond simulant
The Mohs scale of mineral hardness is a non-linear scale of common minerals' resistances to scratching. Diamond is at the top of this scale (hardness 10), as it is one of the hardest naturally occurring materials known. (Some artificial substances, such as aggregated diamond nanorods, are harder.) Since a diamond is unlikely to encounter substances that can scratch it, other than another diamond, diamond gemstones are typically free of scratches. Diamond's hardness also is visually evident (under the microscope or loupe) by its highly lustrous facets (described as "adamantine") which are perfectly flat, and by its crisp, sharp facet edges. For a diamond simulant to be effective, it must be very hard relative to most gems. Most simulants fall far short of diamond's hardness, so they can be separated from diamond by their external flaws and poor polish.