Canvas Preparation
You will need to mix: 50% modeling paste50% gesso
Why do we need to prime the canvas again rather than using an already primed canvas straight away is this. These canvas’s are way too rough, even though they are primed once or twice already. This additional canvas preparation gives you the smooth texture, (similar to an egg shell finish) that helps throughout your entire process of painting in this technique. It will help with your pencil and ink drawings, all the way through and in the final layer, where very small minute brush strokes are used.
Why Modeling Paste? The modeling paste gives the gesso body. It is an acrylic product. Acrylic products have proven themselves to be long lasting and not detrimental to the oil paint film. They should only be used in this canvas preparation or priming and subsequent imprimatur coat that goes on next. Never put acrylic over oils.
With the gesso having the additional body, it is easier to spread and smooth out. It also is easier to remove imperfections. Using straight gesso, (which usually contains a marble dust and becomes very hard, like sanding rock!) makes it very, very difficult to sand and/or smooth out.
Your tools needed are as follows:
A single edged razor blade with its corners rounded off with the grinding wheel. If you don't grind, the razor will gouge out deep cuts in the gesso/modeling layer. The rounded razor removes only the high spots! 
The next tool is a confectionery knife. It too has had it's blade rounded off on the grinding wheel! Below, you can see the texture of a primed store bought canvas. This usually has one to two coats of acrylic gesso already applied. As you can see, the texture is still very bumpy with the weave of the canvas very visible. Your canvas preparation will make this disappear! 
It usually takes 2 to 3 coats. If you use fine linen rather than canvas, you will have less steps. I have never needed more than 2 coats to get a perfectly smooth surface. Sometimes you can find linen priced the same as the canvas! And linen is the better product, so you can charge more for your painting. Applying the gesso mixture is pretty straight forward, you can pour it from the jar, or dabble a few globs with the stirring stick. I prefer the later so I have a little more control of the amount. Spreading the mixture can have its problems. I usually get the 1st coat on quickly of the entire surface and then begin working out to each edge. (Start off with a small amount of gesso mix so you don't have a major mess on your hands! The side's of the canvas, and your work table!) The strokes must be smooth and confident. Pull the knife completely across the canvas in one movement if possible. This will leave only one edge to clear. (either with subsequent knife strokes or after drying and sanding or razor use.) Left over material that rolls off the edge can be quickly be knifed back up onto the canvas surface. The larger the canvas, the more difficult canvas preparation becomes. Start on a small 9" X 12" canvas for your first attempt at this. Each layer will absorb moisture from the previous, so each layer will have a less amount of working time. Working time is how much time you have to spread and pull the knife from side to side before it begins to become sticky. At that point you want to stop and allow the piece to dry. While the first coat is drying, clean the knife for the next coat. The mixture dries quickly, and I use sandpaper to clean off the excess. This should be done away from the canvas as to not drop dust onto the wet gesso. Once the layer is dry, you are now ready to smooth out this 1st coat. It takes 2 steps. The first is with the razor concentrating on the high spots or ridges created by the knife. (These will appear as fine lines unless you hold the canvas vertical against a light to see the actual risen edge). The second step is to sand the minor imperfections left over. Finishing up with some sandpaper to get the smoothest finish always helps shorten the process. I use about a 120 grit paper. Holding the canvas against a light vertically will amplify your view of the surface imperfections. Repeat this process 2 more times, 3 if necessary, to get your egg shell finish for the perfect canvas preparation!
Back to the Lessons Page Expanded version of canvas preparation, stretching canvas the right way. Back to Top of Canvas Preparation
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Here you can see I have worked one side (edge) and have rotatedthe canvas to start the next side. I repeat this process 4 times till the whole is done. Using a hair dryer, I blow dry the canvas to speed up the time to complete. 
