This is the summary of the results of the experiment which I labelled "Two Warsaw Chambers of Numismodeath" (PACHI blog Thursday, 29 October 2015) which 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. 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"'). It is worth looking again at Mr Crawford's photo of the results he said he got from what he did.
[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].
Experiment two duplicates what he said he did. Maybe the fertilisers are different, but basically not a single one of the coins from that experiment looks anything like what Mr Crawford produces as 'evidence'. My coins have metallic patches in between localised spots of thick grey-white encrustations. Only two have any green material on their surfaces, but that looks quite different from what the metal detectorist shows. After three weeks in fertiliser granules, in oblique light my coins have metallic shine, not green crud. Mr Crawford's experimental results could not here be duplicated.
Experiment one used a different methodology, here also the majority of the coins look nothing like what Mr Crawford produced. Only three had a green crud, in two cases superficially similar to Mr Crawford's. But it is only local, not all over the coin, and coins next to them failed to develop this - it is notable that the two which show the effect most markedly were old coins, probably ground-dug (perhaps there was a corrosion initiator [for example chlorides] already in the corrosion before the experiment started).
Even so, although Mr Crawford seems to be saying "look how awful, destroyed coins", having in my own hand the coins that look the same as his and produced by what must be a similar mechanism, I can say with full conviction that those coins are not damaged to such a degree that they are useless as archaeological evidence - however one might regret the absence of that nice smooth patinas of the Tsarist coins and French frank which made them nice to fondle ("piece of the past in your hand"). Perhaps if I have time after Christmas, I will resurrect the Chamber of Numisdeath and damage some more coins in the same way and then have a go at tarting them up to a saleable condition.
The results of my own work suggest to me that amateurs Dean Crawford and John Hooker FSA are being alarmist in claiming that they have 'evidence' of huge amounts of damage to buried artefacts by nasty agrichemicals. Yes, damage occurs, but my experiment shows that even in the same confined space and under the same conditions the effects will differ. To hold out a handful of green coins and suggest this is what inevitably happens when you switch from manure to manufactured nutrients, is simply deceitful. Mr Crawford's experimental results were not duplicated. I invite him to submit a proper account of exactly what he did to get the coloured coins he shows, so we can all try it. Can he do that?