Friday, 27 November 2015

Artificial fertiliser (2)

This is the second of two posts concerning the so-called "Two Warsaw Chambers of Numismodeath" (PACHI blog Thursday, 29 October 2015). This was an attempt to duplicate the results of Dean Crawford's "kitchen sink" coin-colouring experiment which seemed to me suspicious (see my text 'Artefact Hunting, the "Lesser of Two Evils"? More on "Fragmentation"'). I really do not see how the chemistry of what he describes worked and wanted to duplicate his "experiment" to see what would happen. They involved burying fresh and patinated coins in artificial fertiliser for three weeks (as Mr Crawford had described) to see what degree of damage was caused.  For the experimental methodology (so to speak) see the earlier post.

[UPDATE... This post was to be illustrated with photos showing the excavation of the containers, I bought a fresh memory card for that... sadly I neglected to read the packaging, a memory card is a memory card, no? Well, except if its a memory card that needs formatting before use. So, not a single photo is now recoverable. I'll post up pictures of the raw coins when I have calmed down].   

Looking now at the results of Experiment 2: "The Warsaw Dungeon of Numismodeath"...

This mirrors more closely what Mr Crawford shows in his photo, and involved putting fresh coins onto damp earth and then tipping the fertiliser granules onto them and keeping the atmosphere in a sealed plastic container highly humid for three weeks but allowing the air to get to the coins (several already patinated: 5gr 2002 - spotty corrosion breakout, five 2 gr coins from 1991-2004 and one grosz of 2002 and some in freshly minted state, coins of 2014-5 1 grosz, 2 groszy, and and 4x 5gr).

The box was opened, the sponge on the top of the cotton buds was barely damp, but the cotton buds felt clearly damp to the touch and the soil under the fertiliser granules was too and a thin layer of wter had settled on the base of the container, but 25mm below the level of the top of the soil - the coins were at the interface between the soil and the fertiliser (as shown in Mr Crawford's photo). The fertiliser had retained its granular texture (I think this was what the manufacturers intended anyway) but had caked to form a friable crust in which the coins were embedded. The cotton buds were removed and the exposed surface photographed. An odd porous yellow substance is visible at one point, I am not clear what that is and vaguely wonder if it is not a piece of the experimenter's sandwich.

The coins were removed. Unlike the other experiment, there was no appreciable difference in condition according to where they lay in the box, the coins had metallic surfaces when damp, in some places with the original metallic mint lustre preserved, though in several places they had acquired a rainbow-colour patina like the phenomenon called 'cabinet toning' by coin fondlers. This however became less noticeable when the coins dried and we saw the same kind of pinky-grey crust and light overall matting of large extents of the surfaces. Only two coins developed a very thin light green crust on part of one face of the coin (the other being simply darkened). There was no clear difference between the coins that had gone in 'mint fresh' and those which had a patina - in all cases though that patina had gone.

Many of the coins had granules of fertiliser stuck to them, where they touched, the metal underneath was bright and shiny, and it seems very shallow pitting was taking place at the point of contact, in several cases, there seemed to be redeposition of the copper around the edges of this contact zone. There was also crystallisation of a hard granular grey-white material at the edges of the contact zone, which seemed not to be coloured by any copper salts. This material adheres very strongly to the surface of the coin. Under oblique light, in between the islands of this encrustation, the glittery metal can still be seen over about 40-50% of the surface of the coin. The encrustations seem on the whole to be additional material which had migrated between the fertilser granules and crystallised where they came up against a barrier, in this case the flat surface of the coin. I have never seen anything like this on any excavated metal objects from farmland or anywhere else. I doubt you'd find any examples on eBay or the PAS (or UKDFD) dtabase.

Mr Crawford's results were not duplicated.


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