I too received a PM asking for my opinion. While I am absolutely honoured to be considered an expert (thank you, can't say I am one though), I feel Thomas has already answered correctly: in my opinion the coin is genuine too. I feel the wear is correct for a worn Northern-Song cash, and so is the rest of the coin.
White "dirt/paint" can be a bad sign however. A large number of less than decent fake spades and knives are covered in some sort of white plaster like substance (zeno.ru has a couple of beautiful examples of this). On this coin however it is simply the patina with infused soil like material. A large portion of hoard finds exhibit such a patina. As Thomas already mentioned, there are many different soil types, each providing a different patina. We have the so-called "Beijing" patina, characterised by the beautiful green surfaces, but also the slightly darker patina found near the yellow river delta. Some incredible experts can actually tell the provenance by only looking at the patina, me not included unfortunately. My point being; every coin's patina is different. Even within hoards this is the case. My guess is that this coin however was found cleaned roughly, but not too roughly, leaving the "harder" part of the patina intact.
This may just have been Type's points regurgitated into a short reply, but I feel that when two collectors (I dare not call myself an expert) within the same area have the same opinion, it is a good sign.
And to deme; do please show us some of the coins or artefacts you have found! Hong Kong seems like an intresting place to dig!
Kind regards,
Mika
Ps. Thomas, if you are reading this (keep in mind I am not as trained as you are, and I am looking at a tiny picture), is it just me, or does the patina on the coin slightly below the tip of your Bai-bi knife, look a little off? Could be wrong though, but to me it looks slightly doubtful.. Love the entire overview picture though, I should make one too.
Edited by AnYangMan
02/14/2017 4:28 pm