The linseed oil:
I got some "Varnish makers linseed oil" (purified somehow...) from Wood Finishing Enterprises. Any good quality linseed oil will do. "Cold pressed", or "artist grade", etc. And, yes, you can start out with store-bought, so-called "boiled linseed oil".
It needs to be boiled. I have an electric deep fryer thing, from which, I removed the thermostat, so it will keep running. It MUST be watched closely the whole time, and you MUST have the properly-fitting lid at hand, and do it out in the middle of the back yard, well away from anything you don't want burnt down. Do not let it get too hot. Be prepared for flame ups. Start with a quart of oil (or two, doesn't matter much, just adjust the amounts of driers), and bring it to a low, rolling boil. It doesn't have to be raging, just turning over good. Now, you can add drying agents. Toxic, deadly, horrible drying agents (if you're easily terrified by the safety enforcers). About a tablespoon of "white lead" pigment. Lead carbonate. Put it in, and mix it up. If you wish, you can also add some Umber pigment, burnt or otherwise, matters not. The manganese in umbers is also a drying agent, and not toxic. I haven't tried it by itself yet, but you can if you're worried about the period correct deadly lead.... :haha: Oh, and the oil will change color, and smell. The pleasant, familiar linseed oil smell will be gone, replaced by something not quite so attractive. (The lead white and Umber pigments can be obtained from Kremer Pigmente or some other artists' supply house, as can high quality oil.)
Now, here comes the trial and error. The longer you boil it, the thicker it will be (and the faster it will dry, since by boiling it you are essentially "pre drying" it). There seems to be no steady guide for time. For thinner, smoother oil that you can still spread with your fingers and wipe off, try boiling for about a half hour. Test it by dipping in a stick and drawing out a bit, let it cool and see how thick it is when cool (it's always thin when hot). Basically, boil until you reach the desired consistency. When satisfied, turn off the heat and let it cool SOME. You do NOT want it to cool off completely, or you'll never get it out of your pot! I pour it into glass mason jars (has to be hot to pour, but not too hot, as that will break the jars). While the oil is warm, you may add some turpentine. Preferably aged turpentine, as this will aid in drying. Turpentine is aged easily by pouring some into a loosely covered jar and let it sit. Several months/years later, you have rather thick, red, aged turpentine (turpentine itself has varnishlike qualities, and varnish can be made with a turpentine base, though I have never tried it). Some say you can add turpentine to your boiling oil. Now, while it may be beneficial to your oil, I will STRONGLY recommend against doing so. The reason being that a pot of linseed oil that has caught fire will emit 1 foot high flames that are easily extinguished with the lid. Linseed oil with turpentine that has caught fire will blast forth 6 foot high roaring flames of death. Trust me. Keep turpentine away from heat. :wink:
For the first coats, I want the oil thinner so it will penetrate the wood better, and so I can just wipe the excess off the surface of the wood. Yes, it takes a while to dry, and sunlight is absolutely necessary. I can tell by the change in the smell of the wood when it is dry. After getting some of that down in the wood and built up, then I can go to the thick stuff.
My thick oil is so thick it must be thinned quite generously with turpentine to do anything with it at all. With this stuff, you do put it on heavy. For the first application or two, try to not leave a whole lot on the surface of the wood. Let it ALMOST dry (and this stuff dries rather faster than the thin oil!), again, in the sun. Now you're ready for the "hand rubbed" part of a "hand rubbed linseed oil finish". I hope you have strong arms and plenty of stamina. Take some burlap, and cut all the oil off the surface of the wood, using a shoe-shine motion across the grain. Fun. For stubborn spots, you can use a LITTLE turpentine to help get it off, but don't use too much, because you don't want to pull the partially-dried oil up out of the grain. Rub, rub, rub, till your elbows ache. When ALL of the oil is off the surface, then set it back in the sun to thoroughly dry. Repeat as necessary until the grain is completely filled, and the wood surface is smooth with no grain visible in the light. The wood should now have a deep, dark, "wet" appearance. :wink:
Sounds like fun, eh? Actually, it's not too onerous, but the cutting off the oil with burlap is definitely hard work.