Ramesh, welcome to the world of " Ye Olde Mastres" (pat. pend., all rights reserved). !
Some background is in order. "Grinding" has always been a misnomer, as pigment stuffs have always had to be reduced to fine powder before they can be dispersed into oil by mulling.
In the days before manufactured tube colors, pigment stuffs were not micro-fine powders, as they are today, and the resulting paints were much "looser" than the tubed colors we have become accustomed to using through the last 150 years or so. This was largely due to the fact that vehicles cannot be dispersed as well by hand-mulling as in a 3-roll paint mill. Paints made with coarser pigment stuffs would have been necessarily more "lean", as it takes more oil to work smaller particles into paint - it's a question of the total surface area of the particles.
If you don't already own it, obtain a copy of Ralph Mayer's
"Artists Handbook" which includes a table of useful standards for most common pigment stuffs, specifically, the oil absorptive indices of different pigments. Not all pigments absorb or react with vehicles(oil) in the same way, and many require additional amendments (e.g., stearates, waxes, clays, resins, siccatives, treated oils) in order to make useable paints.
The acid number of the linseed oil you are using is also a factor in the quality of paint that results, from its ability to wet and disperse into the pigments, to the nature of the paint films that it produces.
Most beginners mulling paint supply far too much oil, and nowhere near enough muscle. Making paint is hard, miserable work ! (that's why it was the entry level task for child-apprentices in the "good old days") It's also the reason it's nice to have some indication of how much oil any given pigment stuff is likely to absorb in order to be made into good paint.
A good way to proceed is to work as little oil into the pigment as possible, (using the oil absorptive index as a guideline) until you have what resembles clay too dry to "work". When your batch reaches homogeneity at this consistency, lay it by overnight (in a refrigerator is ideal) and mull it again. Ordinarily, you'll find it will reach a good consistency without adding any more oil after a second or third mulling.
The misinformation that tubes of paint that release free oil are "defective" has actually been published in major art magazines . . . by people who certainly should know better. Release of free oil is NOT a defect in paint, the fact is, a lot of "name brand" factory made paints are actually
under-bound (i.e., not enough oil to form an adequately strong paint film). The remedy for "free oil" is to store the tubes up-ended, and of course, one may simply blot away excess oil by squeezing the paint onto paper towelling.
At the end of the day, you will learn much by making your own paint, but frankly, there is no particular advantage. In order to make paint not nearly as good as you can buy, you will certainly spend far more for materials and certainly a LOT more in time that's better spent perfecting your painting abilities.
Not even the old masters made their own paints once they rose above being apprentices! It's far better simply to procure the very best quality paints you can buy from reliable sources once you have learned the earmarks of excellent quality , as well as sub-standard paint.
The highest pigment loads, least percentage of fillers and amendments with the highest quality vehicles are not found in mid-tier, much less student grade paints (which are execrable!) and oftimes NOT by big "name brand" color-makers, but by the smaller, boutique colormen whose products are generally not found at massive discount in outfits like "Cheap Joe's" or "Jerry's Artarama" . . . conversely, the best economy is to buy the finest quality.
Without endorsing any specific maker, the following are examples of colormen whose knowledgeability and dedication to their craft (and to their customers) is noteworthy:
Robert Doak & Assocs., Williamsburg, Old Holland, Cennini, Michael Harding, Vasari, M.Graham . . .
to name but a few who come readily to mind. Doubtless there are a number of others, as well, if you search them out. Incidentally, most of these are sources who are willing to discuss the wherefore of paint making with you, much unlike the huge "name brands" who dominate the market in crafts-stores.
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