HOW TO CLEAN COINS
Tools Needed
A good source of light: A strong directional lamp makes it much easier to see fine details
Brushes: Use a stiff toothbrush or stiff plastic or fiberglass brush. A brass brush is ok too, but be careful not to scrub too hard or you could lose some surface detail or patina
Detail tools: Use a toothpick or straight pin to do the fine detail work such as removing the dirt from lettering and finely detailed portions of coins
Cotton swabs: Used for applying solution and/or cleaning lightly- encrusted surface dirt.
Containers: To hold solutions for soaking your coins
Magnification: As small as some of these coins can be magnification is crucial to clearly seeing between the coin and the dirt. A hand-held reading magnifier is fine although a jeweler's magnifier or lighted magnifier works best.
How to clean them
Soap and Water: The simplest method for use with lightly encrusted coins and for in between soakings of more heavily encrusted coins. Often a quick soap and water rinse is all a coin needs. Fill a small container (such as a coffee mug or butter container) with warm water and dish soap. Swish the water a little to mix in the soap and then drop the coins in. Allow soaking for 5-10 minutes; then swirling the container around a little and then remove the coins from the container. Rinse the coins under warm running water brushing the coins as you do. Make sure they are rinsed thoroughly to ensure all soap residue is removed. Examine coins carefully to determine if any further cleaning is needed. Dry thoroughly afterward if no further cleaning is required
Olive Oil: This is the most popular method although it can be VERY time-consuming. But it usually yields the best results. First soak the coins in olive oil for about 7 days OR longer. The oil will penetrate through the dirt and soften it over time, then take the coins out and dry them. Get a container (coffee mug is good), fill with one cup of warm water and add 1 tablespoon of TSP (tri-sodium phosphate), which is available in most paint stores. Put the coins in this solution for five or ten minutes to remove oil residue. Rinse with water to remove the TSP residue. After this soak/clean process; go over the coins with a brush and your detail tools holding them under your strong light source and magnification as you do. If the dirt still doesn't come off easily get off what you can and repeat the whole olive oil process again and again. Repeat this process as many times as necessary. It is not unusual for this method to require from weeks into months fully clean the coin but it is the best method to keep the coin intact and worth the time and effort as well
Acids/Solvents: I have heard of many different acids or solvents being used such as naval jelly, muriatic acid, or even Coca-Cola or lemon juice. I recommend strongly AGAINST any of these methods (or any other acidic solvent for that matter) as they usually will leave you with a destroyed coin. They may work occasionally and I have heard from people who swear by such techniques but the failure rate is high. So only use as a last option! But your own your own if they are destroyed please do not blame me!
General Advice
Patience is the key element to cleaning up your coins. I cannot stress that point strongly enough! It took 1,500 years or more for the accumulation to build up on them and it does not come off without some effort and time. Start with only a few coins if you've never cleaned coins before to refine your skills. Resist the urge to rush the cleaning process: it leads to shortcuts that can damage the coin. Remember a slow steady drip of water can cut through stone given enough time. The same is true with cleaning up your coins. Slow and steady yields the best results and have patience at all times on and the average cleaning can be from a few days to weeks and up to 6 months depending on how dirty the coin happens to be.
I hope this has helped you all out. If you have any new cleaning ways or comments please let me know or add to this blog.