Forensics is the type of science detectives use to solve their cases. Some of this stuff is pretty gross. I won't go too far into that. I'm starting off today with something that isn't too gross. I'm starting with a bit on, well, to put it bluntly, forgery-type stuff. Handwriting tells a lot about us. In some countries you must give a handwriting sample to buy an apartment or get a job. Graphology is the study of handwriting. It's not scientific, but it's still interesting (and even sometimes accurate!) If you draw a circle above your "i"s instead of a dot, you're probably a person who follows the current fads. If there are big loops, the person is probably imaginative and romantic.
Forgers usually do what they do with the intent to defraud. That can include adding zeros to banknotes, changing the whatever is written in a will, or whatever. One of the different ways of being able to tell if something is different are testing the ink to see if it is different than that of the rest of the document. Holding it up to a certain kind of light works. Chemical tests work too, if you're a chemist.
Handwriting is a little easier to check than typed letters. Grammar, punctuation, and word choice all can hint at the level of the writer's education. Also, forgers sometimes have to erase things. You can't always see where they do that. That's unless you have a microscope. If you really need to know if there are any erasures, you can always get a ultraviolet or infrared light to hold it up to.(I'm joking about getting one, but that does work.)
How accurate is the study of handwriting? Let's look at a story. A psychiatrist, James Brussel, was called to investigate a series of bombings. He read the notes left with the bombs and the police reports. He predicted the man was middle-aged, paranoid, and introverted. He also said the man was likely good with tools, neat, and well educated. He was probably of Slavic descent, lived with an older relative, and when caught would be wearing a double-breasted suit. When caught, George Metesky was living with two older sisters, Polish, unmarried, and wearing a double-breasted suit.