Thursday, January 21, 2016

1/21/16 Report - Preparing and Cleaning Encrusted Coins. Another Front Going To Come Through.

Written by the TreasureGuide for the exclusive use of

Encrusted Coin Found by Mark P.

I received the following email from Mark P. a couple of days ago.

Hi there,

I've been following your blog daily for several months now and have spent some time going back through old posts as well. Thank you for sharing your wealth of information to the public. As a new detectorist, I have learned a lot from you, and I know I am only scratching the surface.

One thing I would like to learn more about are cleaning techniques, so I hope you will share some of that knowledge in future posts. In some of your old posts, you mentioned links on the home page to good resources for that, but they are either gone now, or I am not seeing them.

I'm specifically interested in learning how to clean fully encrusted coins that can't even be identified in their present state. I've seen some photos you have posted on recent finds and they turn out beautifully. But I'm not even sure where to start.

Specifically, I have what is possibly (it's too encrusted to tell) a 200+ year old copper coin that I'd like to clean enough to at least be able to identify it. I am not worried about any value it may have, but I want to be able to identify it and don't want to damage it any more than it already is.

Any advice or links you could provide would be very much appreciated.


P.S. Attached is a photo of my possible 1797 Isle of Man half penny - or you know, maybe it's an arcade token. 

Thanks for writing Mark.  The method I use for cleaning silver cobs was originally described to me by Bill Popp, and I posted Bill's instructions way back at the beginning of this blog.   It got deleted with other very early posts.

Bill encouraged me to use the diluted muriatic acid method on silver cobs, and it worked very well.  It is actually less dangerous than electrolysis, another commonly used method.

The first time I tried electrolysis, I used it on a Buffalo nickle, and damaged it.  Since then I learned to use electrolysis more effectively and still commonly use it on some types of objects such as iron artifacts but use muriatic acid on silver cobs.

You can use the link immediately below to find a description of the muriatic acid method.  I have used it almost exclusively for silver, although I am told it works as well for copper coins.

I have run into situations (two that stick out in my memory) when coins were encrusted with a crust that muriatic acid would not penetrate.

I prefer to know what type of coin I might be dealing with before starting.  I like to know if the coin is silver, copper or whatever.  I also like to have a good idea of what type of coin it might be, but that is not always possible.  You will also want to know if you have something that might be very valuable or that should be treated with the utmost care.  Assume that it is until you have a good idea that it is not.  And when you don't know what to do, don't do anything until you get some direction.

For me, one of the first steps is to soak any coin.  Soaking a coin in water can loosen a little crust or remove dirt.  Use water that doesn't have a lot of chlorine or chemicals in it.  Vinegar wouldn't be a bad choice in some cases.  See how much of the crust will come off with soaking.  After that, try to remove any crust that can be safely removed mechanically.  A jet of water can be helpful and might be better than rubbing.  Rubbing can create scratches.

For heavy crust, I prefer to crush rather than chip, brush, or hammer.  I use pliers, sometimes needle-nose pliers, and squeeze the crust.  If you squeeze rather than brush, chip or hammer, you can apply a very measured amount of force.  Start with very little force and gradually increase the force as necessary, but be careful.  Some of the crust will most likely crumble and fall off. Hitting or hammering the crust is less controlled and more dangerous, but a light tapping can be helpful.

Globs of crust, like that shown on the coin in the top view, can be squeezed with needle-nose pliers. Make sure to not hit the coin itself though. With little globs like that, you might not need to put the coin between the tips or teeth of the pliers.  If you have crust on both sides, you can put the entire coin between the pliers.

With some of the crust safely removed, you might be able to better identify the coin.

After removing as much of the crust as you can by mechanical means, start the acid bath.

I like to keep a close eye on what is happening.  Closely monitor progress.

A paste made of wet baking soda can be used on silver coins after the muriatic bath to remove the black patina.  Some people prefer to leave them black.  I don't like a real silvery look and typically under clean rather than over clean.

I have a lot more experience using Muriatic Acid to clean silver rather than copper coins but have been told that it will work as well on copper.

If you want a very detailed description of various cleaning methods, take a look at the TAMU conservation manual by using the following link.

That might be more than you really want to know, but it will give you a lot of good information.

Hope that helps.


The wind is going to shift this afternoon.  For a couple of days it will be coming from the south. Then as the front comes through we'll have a west wind, and then back to a north wind again.

On Saturday the surf will be nearly flat.  At the beginning of the week, the surf will be increasing again.  Expect something like three to five feet.

Happy hunting,