ozjohn

My latest from Colonial Antiques, NZ. An 1862 CGS 65. Sorry about the photo as I did it on my laptop as I'm away from home.

I have an E book called The Identification of British 20th. Century Silver Coin Varieties which discusses all the varieties of the 1928 halfcrown obverses and reverses with photos also including the rocking test described in this thread. https://www.amazon.co.uk/Identification-British-Century-Silver-Varieties/dp/1445753014I Perhaps this may be of use for this discussion.

I can't fault your half equations. The corrosion process for iron is similar to what I suggested for the 50% silver coins except in this case cathodic and anodic sites form on the iron; surface. A process not fully understood but work hardening seems to be implicated. Water contaminated with sulfurous acid, oxygen etc. forms the electrolyte and you have all the conditions for rust. What I described is one of many corrosion mechanisms and may well be responsible to the formation of verdigris on 50% silver coins if the copper is poorly melted with the silver due to the difference in melting temperatures forming the cathodic sites. The electrolyte comes from handling, sneezing and breathing over coin and the normal atmosphere contaminants . I still think a cleaning (one acceptable to coin collectors) and handling the coins with gloves prior slabbing would protect coins from contamination prior to slabbing and should help to minimize corrosion. From my own experience. I have kept a large amount of old 50% coins in a draw for over 20 years and never noticed the formation of verdigris on any of them. No attempt to degrease them has been done.

Contamination is not the prime cause corrosion. For corrosion to take place cathodic and anodic sites must be present on the surface of the coin and the contamination aids the conduction of electricity between the two sites causing a chemical reaction and thus corrosion. In this case the Cu has not melted properly because of its higher melting point and along with Ag forms the other half of the corrosion cell with a potential of 0.28 v between them ( Cu. valency 1, cupric). If the alloy for the coin blanks had been properly prepared the corrosion would not take place despite the presence of contamination on the coin. Of course removing contamination from the coin's surface prior to slabbing would be a good idea and should be given some thought by TPGs. Given this verdigris is as a result of the manufacturing of the coin blanks prior to the minting process not the slabbing. Of course it is still unsightly and damaging to the coin. In conclusion the seed for corrosion was planted in the coin long before it was slabbed.

Perhaps verdigris formation should be seen as part of the minting process of 50% silver coins as it is most probably due to incomplete melting of the component metals as copper melts at a higher temperature than silver. In theory this should not happen if the alloy is properly made. As for bronze coins the metal used is inherently subject to attack.

Quite right. A high grade coin does not always equate to a desirable coin.

After rephotographing the coin I think the actual wear on the obverse is very small apart from the scratches and given the quality of the reverse I think high AU/low MS is probably the correct grade however due the the strike quality the photo of the obverse the coin is not a thing of beauty although it does look a lot better in hand. The right hand photo was taken at a small angle and does not enhance the effigy to any great degree. One thing I did notice is the middle bar in the E of REX which looks like the forked tongue of a snake and quite different to the E in George and DEI.

It seems this coin has generated the same uncertainty on this forum as it has with me with grades from gVF to MS. Thanks for your comments much appreciated. When I looked at the coin the other day under a LED ceiling light the kings effigy appeared almost fully defined hair, beard eyebrow etc which does not agree with the photo. I'll try photographing again at an angle to see if it picks up these details and post the result.

I've had this coin for a while and find it hard to form an opinion on its grading. The picture was taken using a macro lens in ambient light. I have to say the coin in hand looks much better with the king's eyebrow fully defined which is one of the first points of wear. The reverse looks to be of a high grade. Comments please.

If you look at the 1927 crown the Kings's eyebrow can be seen with the hair of the eyebrow showing. Perhaps on the 1928 halfcrown for some it can be seen while on others it cannot. Only a suggestion as I only noticed the hair on the eyebrow after obtaining a 1927 crown where the effigy is larger and I am assuming this was included in the effigy for the other ME issues. The 1928 proof halfcrown held by the Victoria museum is a cracking coin.

This one looks like a fake probably better than most being offered? No mention of copy restrike etc https://www.ebay.co.uk/itm/Bare-Bust-GEORGIUS-IV-Garnished-Shield-HalfCrown-DIEU-ET-MON-DROIT-1829/312578853060?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D56113%26meid%3Dc65e2f9db94745fd91752f9e5724ce48%26pid%3D100675%26rk%3D2%26rkt%3D15%26sd%3D312578853060%26itm%3D312578853060&_trksid=p2481888.c100675.m4236&_trkparms=pageci%3A848977e4-633c-11e9-a5b4-74dbd18024e9|parentrq%3A399c7e3f16a0ab66e3220cc6ffe4a76f|iid%3A1

And the people who spread this stuff.

This is typical of the c**p that goes around. Straight from my sister's Facebook posts. Typical propaganda ploy to belittle your opponents by branding them as stupid

I recently had a visit from my niece who is a doctor in New Zealand and as it happens she supports remaining in the EU where I hold the opposite view. My niece's answer to that was " of course you are old" . I seems to be the way if you disagree instead of an argue on the merits or otherwise insult your opponent a la Trump voters by the liberals . The other one that seems to figure in the Brexit debate is the leavers were too stupid to understand the issues when while the liberal remainders due to their superior intellects voted to stay.

1919 Florin another coin that I had put in a draw and mislaid. It is slabbed CGS 75. Well struck high grade examples of these coins are difficult to find as the strike quality is terrible in a lot of cases. This one's not too bad with the King's ear well struck on the obverse but the reverse upper shield is correspondingly weak with ghosting clearly visible.