I'm doing some tests with a recipe I found in volume IX of the John Singer Sargent catalogue raisonne published by Yale. This final volume contains an extensive analysis of Sargent's materials and methods written by Rebecca Hellen and Joyce H. Townsend. I highly encourage anyone who's interested in Sargent to check out this series of books.
I'm a purist when it comes to materials because I have tested out a ton of different paints, surfaces, mediums, tools, etc. and always come back to the more old school materials. I've learned that the materials that I use to paint have a pronounced effect on my final work. I also like doing research to learn about some of these methods.
The canvas recipe from this book says to apply a heavy layer of size to the linen (canvas and linen are both fabrics used for painting, but the term canvas can be used to describe a linen canvas as well). Size is a glue that acts as an isolating barrier between the oil ground and the fabric. The size is really important because the oil ground would eventually ruin the linen without it. The first layer of size is heated in a double boiler which you can see below and (following the books instructions) I'll apply a second layer of cold size with a palette knife once this first layer dries.
Apparently Sargent preferred canvases with this heavy layer of size and two thinner layers of ground. I haven't used this yet, so I'll have to report back with the results; but I am guessing that this heavy size layer will cut down on the absorbency of the ground and allow the paint to sit more on the top layer. I'm not sure if I'll like this so I only made two smaller canvases to test it out. It's all about experimentation and seeing what works.
For ground, I use Natural Pigments Rublev Colours lead oil ground. It's a great product and provides a lead surface like what Sargent would have used. I'll report back with the results of this experiment later this week..