Interesting results obtained from a little acetone, a cotton swab and a ruined proof

zeebob

Dad and I were sorting some of his collection that had been sitting for forty years in safe deposit boxes. We happened across a 1953 1/- proof that was just slimed with PVC.

Spent ten minutes with acetone, a half dozen cotton swabs and a 7x binocular microscope. We added a bit of gentle persuasion. Results below.

BEFORE

Link to bigger image

AFTER

Link to bigger image

(Yea, I see the spot at seven o'clock. Removed it.)

lordmarcovan

You have a future as a coin doctor! *Ahem* ... I meant conservator.

Nicely done!

canadacolornut

Great results; and nothing wrong with that kind of treatment in my opinion since you're really
only getting rid of a foreign substance that impairs it.

Can you be a little more specific?

Did you rinse the coin between swab treatments? If so in what-water, alcohol?

How long did you leave the acetone on the surface before rinsing it off?

This problem is inherent in Canadian coins that were placed in cardboard holders with cellophane wrappings.
The cellophane causes a milky, unattractive kind of toning(or simply contamination) to cloud the surface
and will always bring the coin down a point or two with a TPG.

Appreciate any further tips.

Thanks

zeebob

I have found that soaking for days in acetone isn't particularly helpful.

Currently, my approach is to place the coin in a shallow glass bowl and cover the coin in acetone.

Next I use two swabs (these are cotton wrapped on a wooden stick - no glue used to hold the cotton to the stick - acetone dissolves glue and the residue will end up on the coin). One swab in my left hand applies gentle pressure to keep the coin in place while my right hand swab GENTLY rubs away the surface contamination. We don't want the coins to slide around against the glass bowl. This process can take anything from 20 seconds to ten minutes.

After that, I pull the coin out of the acetone and wave it around (sometimes accidentally losing my grip only to watch the coin fly across the room). This drys the acetone. Sometimes there is just a bit of yukky that shows up where the acetone last evaporated. I believe this is simply dissolved contamination being deposited on the coin.

Next, I take two CLEAN swabs and some clean (right from the can) acetone and repeat the prior gentle rubbing, using only a WET swab. For this, the coin is just set on a paper towel, not submerged in acetone. This takes up any little reside left from evaporation and allows a little clearer view of the surface if additional areas (like inside letters) need some, dare I say, scrubbing (gentle teasing of the contaminant off the surface is more like it).

I work under a 3.5-40 power binocular microscope.

I have tried both IPA (isopropyl alcohol) (70% and 90%) and distilled (and DI) (and both Hot and room temperature) water rinses. Near as I can tell, air drying acetone with careful inspection is the best. All other methods have left me with more residue or water spots than acetone.

Now, there is one trick I have learned. That is that if you have a coin soaked in acetone and then air dry it, often the evaporation seems to push the surface temperature of the coin below the dew point so water from the air condenses on the surface. This leaves little spots and stains.

I use a hot air gun (like a air drier) to keep the coin warm during heavy evaporation.

The second round of swabbing (when the coin is not submerged) will usually not generate condensation.

canadacolornut

Thanks for that Zeebob. I have tried this thing several ways and am anxious to follow the example you laid out.

It never occurred to me to let acetone dry on it's own. I thought it would continue to work on the surface
until I rinsed it off with result of the kinds of spotting you alluded to.

Great information!

Thanks again.......

zeebob

Acetone is highly volatile. It will completely evaporate in seconds from the surface of the coin. The only thing left behind will be gunk that is NOT acetone (like residual PVC or glue or other contaminates). The second treatment with a swab seems to allow the acetone on the swab to wick up the yucky stuff onto the swab while leaving just a fine thin layer of acetone to evaporate on the surface of the coin. A fella just has to be careful to have a light touch so as to not leave scratches on the surface of the coin.

1960NYGiants

I rather like the outcome on that coin. Is the lighting condition the same for both sets of photos?

Lancastercoin

You might want to try buying a squirt bottle for acetone (sold at chemical supply houses) so you can rinse the coin with clean acetone after it comes out of the baths. That way any dissolved PVC won't be redeposited when the solvent evaporates. Be sure to have a well ventilated area when using streams of volatile solvents.

zeebob

A rinse bottle is an excellent idea. I may just have to do that! Thank you.

Regarding the lighting question, the answer is "almost".

The same lights, camera, lens and mechanical setup were used. I think the exposure was one click (or maybe two) faster for the conserved image (so maybe the first image was shot with 1/40 and the second with 1/50 or 1/60). Also, to be able to get the colors in the second image to show up, the coin was tilted about thickness of a dime.

In the first image, you can sort of see there is color under the slime (look for the yellow on the reverse shoulder, arm and leg). But the gunk prevented the color from coming through.

The images of shot of the conserved coin that were in exactly the same orientation as the pvc covered coin show color and clear surfaces but the color the eye sees doesn't really come out until the coin is tilted just a smidge.