Though dirt is dirt and sand is dirt, there are clearly differences in the
quality of dirt which can be on a coin.
"Typical" grey-to-brown spectrum "dirt" is generally easy to spot,
as is the wonderful "
red Syrian sand". It gets tougher with the beach-sand coloured dirt.
I have coins from the Middle East and coins from Lower
Austria that both appear to have a sand coloured dirt coating on them. I bet that if I showed photos or some coins in hand few could guess which was which. (Obviously more of a Middle Eastern lot have this colouring while fewer of the Austrian lot do.)
The Middle East coins actually have what I would call the desert
patina or desert sand. The dirt is very dense and made up of
very fine particles when you look under magnification. It also tends to adhere very well to the coin surface, which is often a wonderful black or blackish
patina. Thus I can use the "wet cleaning techniques" you find discussed on this site and end up with a so-called "desert
patina" coin (which might be better known as "desert effect" as it is really a partial cleaning to contrast a sand coloured dirt with a dark black
patina). Not all Middle East coins will clean up this way, on some the dirt just flakes off. Also I can not get the same fantastic results as Kevin or Salim or many others.
Sadly, despite looking similar, the Lower Austrian sand coloured coins simply do not behave the same way as the Middle eastern ones despite looking the same in hand. The dirt is not so
fine nor as compacted as the Middle Eastern sand coloured dirt. The coin
patina is medium to dark green or even brownish under the dirt but almost never black. The wet cleaning technique yas yet to yield decent results on these coins. The dirt
comes off more easily than the Middle Eastern stuff and often in chunks. Therefore it can't be "
reduced" or "thinned" in the same way to yeild the desert
patina look.
So renegade, the first thing I would do is figure out where your coins are from. If the Middle East then you may be able to leave the dirt on any beach-sand coloured ones. If European then the dirt will probably have to go.
Another diagnostic is to scrape a little of the upper surface of the dirt away with a sharpe blade. I find that the European sand coloured ones will reveal the same colour or even a more pale beige underneath the top layer whereas the Middle Eastern ones will show a brighter yellow or even orangish colour under the top layer of dirt.
Shawn