It is not as silly as the it sounds. It does pull air out of the interstitial spaces of the coin or the dirt cover, and that will be filled by the water or oil.
Here are the disclaimers 1. Oil has a high viscosity at normal room temperature, so to be more effective, it needs to be heated. that has been the problem with using olive oil, it may take a year just to penetrate 1 mm.
2. Water alone is often blocked from entering spaces because of its surface tension. The surface tension of water may be changed by using additives, most are the same as simple
dish washing soap, or in the photographic world Photoflo .
3. Neither water
nor oil are very compressible, for our use they are incompressible. The easiest way to remove the air from trapped pockets of a coins
flan or crust is by using heat. Hence the use of boiling, the air expands and the bubble will release once it's bouncy overcomes the surface tension, this does leave a void, and it will be filled by the surrounding liquid. This speeds up the process.
4. Scrubbing : this removes old softened surfaces and allows the water or oil to 'attack' the the new
area and continue the processes. However, the cleaning solution will become depleted, as the chemical balance changes, hence the need to change the oil, water or cleaning solution. At the start the solutions will saturate faster than later as the coin becomes cleaner, there is just less of the crud to dissolve.
These comments are somewhat simplified, but are accurate. The use of vacuum to clean coins would require a lab unit, capable to draw a vacuum of at least 30 inches of mercury or about 900 mm of mercury. That is about 90% of atmospheric pressure.
Bruce
