If you asked people about kohl, you get answers such as "Cleopatra used it." or "Its nice and creamy", or "Its easy to blend" because that is what we associate with it. Real kohl is none of these things except used by Cleopatra."
Kohl has been around for a very long time. It made its way to Europe in the 8th century. Since good quality kohl is made of ground up galena (lead sulphide) or stibnite (antimony sulphide), it is not legal in the United States because they are poisonous due to the lead in it. Since they are toxic, the FDA will not approve their use in the United States and what is marketed as kohl is actually a color. However, if you are in the Middle East and you see it, that may have the toxic ingredients so it is best to ignore it.
Historically, the term kohl referred to eyeliner made from a variety of ingredients such as the two minerals already mentioned, carbon black, or iron oxide. It became common to call any black eye lash, or brow product kohl including those that were made of ink. Traditionally, kohl is used in the powdered form which western cosmetic companies have introduced but it didn't do well since most people do not know how to apply a powder to line the eyes.
The kohl we see here in the United States refers to a specific shade that is not black. It is actually more of a grayish black and is the same color as pencil lead. The shade comes from chemists trying to match the real deal and to make the powder solid, they add wax so it's like any other eye liner. If you find a product that alleges to be real kohl, it is probably ground up charcoal if it is in powdered from. If it is in stick form, it has things added to make it stay in that form but if you want it to be able to smudge, then look for that effect when you buy your kohl.
So if you want to buy kohl, know that it really refers more to the color than the actual product. Let me know what you think, I'd love to hear. Have a great weekend.