Hey, enialadam, you beat me to it! Thanks for stating this off. There’s quite a bit of ground to cover, so hopefully this thread will be helpful to people. I was making a few notes last night of some things to share.
Sizing with Shellac:
Outside of rabbit skin glue, shellac is one of the best “sizing” liquids I use on firm supports (wood.) Its easier to handle in that you dont have to keep it warm. Also “no rabbits were harmed during the making of this painting.” There are commercial brands of it in liquid form, or in dry flakes that you make liquid with denatured alcohol. The flakes are more economical in terms of volume, but the liquid form is a bit more convenient. Get bleached (white) shellac that is wax-free. A commercial brand that is bleached is hard to find. Shellac is an organic product (made from bugs) so it has a limited shelf life, except for the commercial brands, like Zinsser, that claim their cans to last up to three years. What they use to make it last that long, I dont know. Thats a reason I prefer the flakes.
Washes of oil:
Its not advisable to thin your oil paint to a watery consistency. Doing this with a solvent like turpentine or odorless mineral spirits (oms) to a point where its very runny will cause the pigment to have poor adhesion. Oils are not watercolors. If you want a very thin look of paint on your surface, you can apply it with a rag by wiping very thinly without having to dilute it, and get very much the same result. This is a technique I use often for my underpainting tone. Ill mix up the shade I want, dab it with a brush in random spots of paint, and then scrub the surface with a rag. If that rag is SLIGHTLY damp with solvent, this works a bit more easily. Some colors are also very transparent right out of the tube, and work well for this effect.
Similar to the problem of washes of oil being a no-no, there are certain textures you might want to get with paint, which would be difficult to achieve without a very fluid medium, like splatters or drips. Some manufacturers make paint that is very fluid. Unlike the typical “buttery” consistency of oils, you open these up and the paint practically drips out. Many painters hate this and discount these paints as poorly manufactured product and unusable, but sometimes you may want a very “wet” paint that still has a concentrated color. When you want to draw long lines, these paints would work well in addition to being fluid enough to cause splatters with an old toothbrush or stiff bristle brush. Sennelier is one brand that tends to be very fluid in all the colors Ive tried.
That brings up another tip: how to paint long lines of concentrated color. A heavy loaded brush of opaque paint only goes so far, and if you thin it down to go further, its not opaque enough. If you dont have any of that fluid paint handy, draw your lines in ink. Shellac based ink is more compatible with oil than carbon (sumi-e) or water based ink. Acrylic ink wont adhere to oil. With a little study you can make your own shellac ink. Glazed oil paint on top of the ink would dull it to some degree but still allow it to strike through. Many ancient egg tempera paintings overlaid with oils were made this way. You could try colored inks as well.
This is a question that comes up often: whats the best way to keep your brushes clean? There are some specialty soaps that are designed for brushes (Pink Soap, Ugly Dog, etc.) that work well, but still tend to leave paint or oil behind if used by themselves. Solvents can be very effective, but the fumes can be unpleasant to work with, or dry out the skin by removing the oil on your hand. In that case Id follow up with lotion. Turpentine can also be rough on hairs. OMS or possibly kerosene would be a good cleaning solvent. Use these with care.
To avoid using solvents for cleaning, a method I prefer for brush cleaning is to use oil. I wipe off as much of the paint first as I can, and then dip the brush in a tiny bit of oil, rubbing it into the hairs. Finally I wash it with brush soap, and pat it dry. That always seems to get the most paint out. I use is mineral oil (unscented baby oil) since it seems to wash out best. This is non-drying oil, so I want to be sure and get as much off the brush as possible. You can also use a painting oil medium, like linseed, walnut or safflower, but besides being more expensive, these are drying oils, and a little bit left in the brush, while harmless to your painting, can cause the brush to get stiff. One thing that helps remove excess oil is acetone, which you could use before soaping, but that has strong fumes too. I have difficulty believing thered be much mineral oil left behind after washing that would cause any painting problems, but its a risk worth mentioning.
If anyone has any specific questions, feel free to speak up. I’ve been using oils for many years, so if I don’t know an answer, I’ll try to lead you to a good solution.