Coating of dirt vs. Sand patina

[renegade3220]

How do you tell the difference between just a thin layer if dirt that should be removed and a sand patina? Is the sand patina smoother, stronger, withstands gentle brushing? Or what!? I can never tell if the dirt should be removed or if it should be cleaned as though it has a sand patina.

Thanks in advance!

[Jay GT4]

Sand "patina" is not really patina at all but a layer of dirt.  Depending on what kind of dirt it takes on different colors like the Syrian red that is so sought after.  The way I look at it, anything that makes the letters or devices stand out should stay (or rather can stay).  Many coins look better with this "dirt" in the fields, it gives a nice contrast especially if the coin is worn.

[renegade3220]

Aye, that is what makes it hard. Both are just dirt but one should go and one should stay...

[areich]

There is no 'both', the difference is just what people call it. Unless it's a fake, glued on 'desert patina'.

[SC]

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