CLEANING ROMAN COINS   

Before you start cleaning your coins you will want to assemble a few tools and some chemicals.
Tools:  A good source of light is essential.  Craft shops sell magnifying lights that are very useful, especially if you do not have a stereo-microscope.  Empty baby jars are very handy for holding liquids and soaking coins.  You will need an old toothbrush for scrubbing the coins, toothpicks or dried rose thorns for picking out bits of dirt, and cotton swabs for working on small areas of a coin.  Remember that ancient coins are fairly soft metal, bronze, copper, silver, or gold.  You do not want to scratch the surface of the coin while cleaning it nor do you want to remove any patina that may have built up over the centuries.  Your object is NOT to reduce your coins to shiny like-new condition.
Chemicals:  Most of the dirt on your coins will yield to soaks in distilled water or olive oil.  Avoid tap water, the chemicals in tap water can harm your coins and destroy any traces of patina that may remain.  More encrusted coins will clean up after soaking in olive oil.  Use the least expensive oil, not extra virgin.  Very persistent dirt can be removed with WD40 or a combination of baking soda and vinegar.  These last two should be used only as a last resort as they can change the colour of the patina.  Vinegar and baking soda can also worsen pitting on already pitted coin surfaces.

THE CLEANING PROCESS
Sort your coins before you start cleaning them.  If you are very fortunate, you will have some that will need very little cleaning to be recognizable.  Keep these coins in a separate jar as they will not need much work.  If you only have a few coins, put them in a small dish or baby food jar and cover with distilled water.  Allow them to soak for an hour or so then pull one out and rub it with you fingers to see if the dirt is softened enough to remove.  If your fingers get soiled, use the toothbrush to scrub away at the surface.
Do this with all the coins, one at a time, rinsing each one in more distilled water and drying carefully with paper towels.  Examine each coin under magnification, either a hand lens, magnifying light, or stereo-microscope.  Some of your coins might be pretty clean just from the water soak.  If they are still encrusted with dirt, a longer soaking, over night or for several days, in fresh distilled water might do the trick.  Repeat the soaking, scrubbing, rinsing, and drying a second time.  Coins that are still encrusted wit dirt and corrosion should now be put in olive oil. Use a container that has a tightly fitting lid so that you don’t spill the oil accidentally.  Dirty olive oil is very messy to clean up.  Let your coins soak in the oil for a day or more.  You can pull them out, brush them with the toothbrush and blot with paper towels, and examine them under magnification.  As the dirt comes off, remove the clean coins from the oil but return the still dirty ones for more soaking.
As the dirt and corrosion comes off the coins you should be able to see images and inscriptions.  If, as you work you way through the cleaning process, you cant see anything you may have to accept that you have a worn-out slug, a coin that has been through many hands and all the images are rubbed smooth.  Fifty years of constant circulation is enough to remove a most vestiges of relief from a coin.
Patina is not present on all coins.  It is a coating that develops on metal after many years of use.  It can be greenish, brownish, or greyish in colour and many collectors consider it one of the beauties of ancient coins.  A coin with excellent patina can be forgiven a slightly worn image. For instance NEVER do anything to a coin that will remove the patina or change its original colour.
Coins that show good images, patina, and some inscription are worth a more careful examination under magnification.  Here is where you will want to start picking with a toothpick or dead rose thorn.  Work carefully under magnification and try to dislodge bits of corrosion from between letters and around details.