Here is a demo on how I make my own oil paint. In the pic above you can see everything laid out except my dust mask. Particles can become airborne and a dust mask is important.
To make oil paint you need:
linseed oil-cold pressed
(I use my own hand made linseed oil)
a couple palette knives
First I lay out an amount of dry pigment that I think will fit my empty paint tube. I lay the tube next to my pile to measure. (real scientific!)
Next I make a pool of oil in the middle of the pigment. The white in the pigment is a touch of calcite that I've mixed in. I like adding calcite to my oil paint, it adds a touch of transparency and extends the paint. That is a definite bonus for creating your own oils, you can customize them to your liking. I also add a touch of sun oil to raw umber, in combination with the calcite I get a very specific texture that is great for under-paintings.
I use a palette knife to mix the oil and pigment into a dry mixture and place it in the upper left corner of my glass plate. I will now mull small amounts at a time to the proper consistency. I tend to make thick mixtures because I know I will add a different medium to this when I am painting and I don't want slippery, thin paint!
I continue until I am through the entire mixture, placing finished paint to the top right on my glass plate. I sometimes go through the mixture twice, in case I need to add more oil if it's very dry, or more pigment if it's too wet. Once you start mulling the paint it changes texture and different pigments react differently after coming in contact with oil. Some will thin out considerably.
A 50 ml tube will take about an hour to mix correctly, it's time consuming but not difficult.
A finished mixture of raw umber, ready to tube!
Below you can see the dramatically different textures of different pigments, each unique in particle size and handling ability. Not all paints I make end up on my palette, but when I discover something that works for me it becomes a staple that I rely on in my painting process. That has been the best discovery of all, how amazingly unique each pigment is, and how you can manipulate it's handling properties with different oils and extenders. Experimenting takes time but is completely worth the effort.