On the Return of a PCGS UNC Cleaned Grade


Given the time I spend responding to PCGS graders, I thought it might be worthwhile sharing so collector’s can see my thought process. Doesn’t mean I’m necessarily right – I simply review the data and interpret the outcomes that I believe are correct. Names remain anonymous. Cheers, Les

The Email


As for the detail grade, I’m prepared to respond to PCGS on this score:


Starting with the definition of the grade according to PCGS:

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I’d like to see what evidence PCGS has of abrasive cleaning causing surface damage. I can certainly given the coin a good going over with the microscope when it returns if PcGS cannot hold onto it.

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My above coin has clearly had its fields wiped and given the toning colour, was likely held by its owner. The six & 7’o’clock region suggests contact with oils. The obverse high points have been wiped or fingered. Such contact is always going to accelerate oxidation. Happily the build up is relatively stable.

The following coin was recently graded SP64RB. I’d hazard a guess that it too has been wiped. Splotchy patches of deep colour is not a high confidence illustration of natural toning.

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Similarly, natural toning does not begin on a flat surface like a field of the coin below. Oxygen molecules lodge themselves in small steps and recesses and then continue to bond molecularly under the right circumstances, spreading across the coin.

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The uniform blue toning reaching in between the lettering –  which retains mint red colour – is a red flag that the fields were wiped.

Below is a wonderful example of natural toning. 2nd cycle Cyan on the left has built up to 3rd cycle blue on the right. The high points are showing appropriate “elevation chromatics” (see http://jhonecash.com/coins/tonedmorgans.asp#ntvsat) Lemon yellow and sunset  yellow are building over the Cyan around the lettering – a good illustration of molecules bonding in the steps of the fields. I’ve placed the Sunnywood chart on its side so you can see from left to right the natural progression of colour.


I artificially created the following toning and observed how it spread across the coin. Contact with the wood triggers corrosion by acetic acid on the rims, which then continues to build inwards along the fields to the centre of the coin. It’d take another year or two to completely tone this coin, although I’ve since given it a coating of Verdichem to halt further oxidation and keep it as an example. The colour toning is correct. It’s simply been accelerated by Darwin’s humid heat on a windowsill and chemical contact with fresh wood.

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So back to PCGS and their “cleaned” grade. If it’s not abrasive cleaning and the toning does not detract, it arguably deserves the numeric grade. Something I’ll be researching further on and responding to PCGS when this coin returns.

Feedback welcome. XXXXX is cc’d in.