Straight razors with open steel blades, also commonly known as cut-throats, were the most commonly used razors before the 20th century.
Straight razors consist of a blade sharpened on one edge. The blade can be made of either stainless steel, which is slower to hone and strop, but it is easier to maintain since it does not stain easily, or high carbon steel, which hones and strops quickly and keeps its edge well, but rusts and stains easily if not cleaned and dried promptly. At present, stainless-steel razors are harder to find than carbon steel, but both remain in production.
The blade rotates on a pin through its tang between two protective pieces called scales: when folded into the scales, the blade is protected from damage, and the user is protected. Handle scales are made of various materials, including mother-of-pearl, celluloid, bone, plastic and wood. Once made of ivory, this has been discontinued, although fossil ivory is used occasionally.
Disposable Blade Straight Razors
These razors are similar in use and appearance to straight razors, but use disposable blades, either standard double edged cut in half or specially made single edge. These shavettes are used in the same way as straight razors but do not require stropping and honing.
The first step towards a safer-to-use razor was the guard razor – also called a straight safety razor – which added a protective guard to a regular straight razor. The first such razor was most likely invented by a French cutler Jean-Jacques Perret circa 1762. The invention was inspired by the joiner's plane and was essentially a straight razor with its blade surrounded by a wooden sleeve. The earliest razor guards had comb-like teeth and could only be attached to one side of a razor; a reversible guard was one of the first improvements made to guard razors.
An early description of a safety razor similar in form to the ones used today is found on William Samuel Henson's 1847 patent application for a comb tooth guard. This guard could be attached to a straight razor or to a razor "the cutting blade which is at right angles with the handle, and resembles somewhat the form of a common hoe."
Around 1875 a new design with a smaller blade placed on top of a handle was marketed by the Kampfe Brothers as "the best available shaving method on the market that won’t cut a user, like straight steel razors."
Read more, here.