I saw so many painters just start to paint right on the canvas without even make a sketch, but they do a skecth with oil, but it is necessary to have a lot of practice to do that.
If you are starting to paint i advice you to do always a sketch it is going to pay you off at the end, because I saw some painters making mistakes and they had a really bad time trying to correct it with oil, to be honest that happened to me a couple of times and it is very frustrating to do the corrections.
A sketch, in other words a draft is a preliminary and schematic drawing of the object to be painted. At this point we should not worry about the details, rather just represent the main lines to understand the object or main figures to be painted. Remember that a sketch is a freehand drawing that are made without any technical instrument and it will guide you through the painting process.
The sketch, in oil painting, is used by many artists to make the previous strokes of what they are going to paint, and then start to give it color. For people who are starting to paint with oil, it is advisable to make a sketch first before starting to paint.
And what do we do the sketches with?
Charcoals There are several available means that we can use to make a sketch, in the case of oil painting we recommend the use of charcoals, as these strokes are easy to erase. All you have to do is wipe it out with a cloth and the strokes marked on the cloth will disappear. This features also helps us that if we make mistakes these can be corrected with ease.
The sketches can be classified in two ways which are:
Simple: is the drawing of the first idea that comes to mind. In this type of sketch only the idea of drawing with simple and poorly defined features is captured and at the same time if you are planning to paint with no details this kind of sketch would be ok for you.
Detailed: this is a sketch of more quality, in this type of sketch can be used technical instruments. The drawing is sharpened a little more, more details are captured, and the objects of the drawing are clearly defined. I use this type of sketch because I want to capture all the small details and even sometimes I go more detailed in my drawings, but it would not be considered as a sketch.
In summary the sketch is one of the steps that is recommended before starting to give color to your next work done with oil.
Remember to spray some fixative over you sketch.