When you apply oil to a shell, some of the oil actually penetrates into the substance of the shell, and some of it remains on the surface of the shell. Getting oil into the crystalline structure of the shell is the objective. That's why some people dilute the oil with a solvent - to make it less viscous, so it can penetrate more easily. Once oil has filled the porous spaces in the microstructure of the shell, you want to remove the residual oil that remains on the shell surface. Otherwise, the shell looks and feels oily, leaves oil spots on your labels and cabinet drawers, and attracts air-borne dust like a magnet. With a smooth shell like a Conus or Cassis, oil can be applied with your fingertip, or a cloth or brush, and all the residual oil can be removed simply by wiping with a clean, dry, absorbent cloth (I prefer old bath towels). But with a heavily sculptured shell like a spiny Murex or Spondylus, or a rough-textured shell like a Morum or Morula, you need a small brush to get the oil down into the pits and crevices of the shell. And once the specimen is oiled, you cannot wipe off all the residual oil. For such shells, I use warm water, in a fine, high pressure spray (one of those extension hoses that come on many kitchen sinks) to remove excess oil. If you use undiluted mineral oil, you should leave it on long enough to let it penetrate, before removing the excess oil from the surface. Probably 15 minutes or so is enough. If you use diluted oil, you should allow the solvent to evaporate before removing the excess oil. 15 minutes is usually enough for that too - most organic solvents are pretty volatile. In using such solvents, don't neglect health considerations. Remember, when the solvent evaporates, it doesn't "disappear" - it mixes into the surrounding air, which means you will be breathing the solvent if you evaporate it indoors. Also, some solvents can be absorbed through the skin, so oil diluted with organic solvents should be handled with care. Obviously, the level of potential danger from either absorption or inhalation depends on the particular solvent used, and the amount of exposure. Something like benzene or chloroform or gasoline is highly hazardous, while xylene or kerosene or mineral spirits is RELATIVELY safe. Also, keep in mind that many of these solvents are moderately to highly flammable, even though the mineral oil itself isn't. Paul M.