I’ve come to a tentative conclusion. I want to set up easy preferred access to two kinds of solvent, one for the tractor bay in the barn, and the other for the shop indoors (where I also do electronics, handle some laboratory equipment, and other odd stuff).
In the shop I encounter a wider variety of things I need to clean up. There are lubricants as well as whatever grime is on metal stock. But there are also soldering flux, adhesives from labels and gaskets and little assemblies, and contaminants I never know the origin of. For this stuff, acetone is often useful (as many people here also note). But, acetone is pretty polar as solvents go. There is a strategy in creating solvent systems that says you should mix solvents that are pretty different from one another, because the mixture will handle a broader range than any of the single solvents can.
There is a concept known as “Hansen solubility parameters” from a 1967 PhD thesis. You can locate any solvent on a triangular map according to three parameters: the energy from dispersion forces, the energy from dipolar intermolecular forces, and the energy from hydrogen bonds. You can also locate any contaminant on this same triangle. The closer a solvent is to a contaminant in this map, the better it will work. And, a mixture of solvents that are widely spaced on this map will be able to remove contaminants near any of the solvents.
Closest to one point of this triangle are highly polar solvents, which deliver big on the dipolar intermolecular forces. The ketones, including acetone and MEK, are in this direction. Since acetone is cheap in fairly pure form, has fairly low toxicity, and dries quickly with low residue, and like many say is a broadly useful solvent, it’s a pretty obvious pick. I could do a little better with acetonitrile but I’ve never played with the stuff or seen it for sale, so, enough’s enough, let’s say acetone.
But toward another point of the triangle are things with high dispersion force. Solvents out this way include hexane, white spirits, xylene, toluene, and benzene, the aliphatics and the aromatics. They actually make more effective solvents for petroleum based lubricants and residues from petroleum fuels. Therefore I’m picking something out here to mix with my acetone. Because benzene is so toxic, and xylene is a bit slow to dry and greasy feeling, I’m going with toluene. Nowadays, toluene has a bad name and limited availability because kids tend to use it to get high, but this is here in my own shop where there’s nobody to do that, so that’s no problem. I also thought of hexane but I’m not sure if it might dry too quickly. And I don’t want to analyze this more than is worthwhile. I know toluene and it’s satisfactory, so we are going with toluene. I’ll say more about white spirits in a bit.
The third point of the triangle is where hydrogen bonding forces predominate. This is where water excels, and the alcohols also do well. Removing salty sweat and grass stains is out in this corner, like various other laundry challenges. But adding a strong hydrogen bonding strength solvent to a system can have negative effects like causing the other solvents to separate out into two phases, and drawing atmospheric water out of the air, encouraging rust and corrosion. And the kinds of cleaning challenges that live here are less often what we deal with mechanically, and more what we hose off in the driveway with Simple Green. Well, I have water and 91% isopropanol and various soaps and detergents conveniently available anyhow, and for some contaminants I’m quick to reach for them, so let’s say I have these needs covered already.
Therefore, for my strong, quick drying, low residue, versatile solvent in the shop, I’m going with a 50/50 mix of acetone and toluene. I also found an article that described this blend as an ideal laboratory solvent for dealing with a broad range of unknown contaminants. Sounds pretty good to me. I’m going to fill my new 1 quart plunger can with this in the shop.
Now, about the tractor bay in the barn, let’s get back to white spirits. There is more or less of a family of solvent mixtures distilled from petroleum. These petroleum distillates come by different names including paint thinner, naptha, white spirits, Stoddard solvent, deodorized whatever, and even charcoal lighter fluid. They are toward the high dispersion force point of the triangle, but then so are other petroleum products like lubes and fuels, so around a tractor or other power implements they are a pretty useful product. I’m going with a light, deodorized distillate on this one. Safety and cost and availability are all excellent. It will be a bit different from the shop mix (acetone/toluene), so if one system doesn’t work well I can take a quick stroll to try the other. This is why I didn’t pick the light petroleum distillate for inclusion in the shop mix. Besides, these light petroleum distillates tend to be safer on paints and plastics and other things I don’t want to ruin. And they’ll be kind to my white shirts (in fact Stoddard solvent was originally made as a drycleaning fluid for nice clothing). This is what I’m putting in the two quart plunger can in the tractor bay. And I’m picking something deodorized. I’m done with using gasoline and kerosene, and stinking all day.