Help: How to clean crusty, sediment encrusted metals...(think barnacles!)

[ROIGuy]

I went beach hunting yesterday and got some "hot rocks" or so I thought. Not sure what they are, because they're so heavily encrusted with sediment.

I think these are beyond soaking in lime juice or vinegar and baking soda. Any ideas on how to clean this stuff? Should I use a dremel to get off the larger sediment THEN soak it in some solution?

Here's the photos. PS----found a 'coin' that is both smaller and thinner than a dime. I haven't attempted cleaning it yet because I'm on vacation and don't have a lot of supplies.
Any idea what it might be? Maybe there's someone here with better eyes than mine but it almost looks like there could be some writing on it.

Images:

 

Amazon Forum Fav 👍

A History of Mining on the Kenai Peninsula, Alaska - Grab it through Amazon!

[cudamark]

The second and third photo looks to be a crusty zinc cent. The last two probably a copper cent. If true, I'd dump the first, and tumble the second, after doing a preliminary clean up to determine type and year.

 

[FloridaSon]

Don’t dremel use a wooden toothpick first. Some blunt the end. Don't throw until you know.

 

[zigzag]

I use Sno Bol toilet bowl cleaner. Put the item in a plastic lid or something just big enough and cover it with toilet cleaner. It works just like when you put baking soda on a corroded battery post. I probably wouldn't do it if I thought the item was somthing real valuable.

 

[Rum Tide]

Electrolysis

 

[ROIGuy]

I'm going to try the 2nd method in the video while I'm still here. The method he described is heating the coin then putting it in cold water to see if I can shock some of the heavier sediment off the coin. Then I'll try electrolysis when I get home.