advice required on coins with multiple colors for patina

[Johnny]

I could use some advice on coins that have more than 1 color showing for patina  as far as cleaning goes

for example the coin attached to this has  black, green and brown spots on the reverse . all appear to be patina but could be some kind of dirt or mineral deposit

they are in layers with the brown at the bottom then a mix of green/black blotches on top

do I clean to the brown color , or do I stop when I hit green ?

I really don't want to mess up this one as the details are fantastic ( looks a lot better in hand)

the coin is still unattributed VLPP from constatine I ( the great)
with   :Greek_epsilon:sis  and an S in the altar

thanks for any advice

[Johnny]

here is a clearer pic

[awl]

I would clean around the brown because from my experience it is extremely hard to remove and it usually ends up damaging the coin away.

-Adam

[Johnny]

Thanks Awl

I was picking away at it and I have to agree

strip it right down to the brown patina is gonna be tricky. I really don't want to wreck this one. I see why Victor has a liking for these vlpp very nice craftmanship with lots of detail

on an other note,  what causes the patina to go to different colors  in this case green and brown,  The black is encrusted dirt and is flaking off
minerals in the ground ? different metals in the coin ?

[Mark Farrell]

Different patinas can be caused by almost anything, including soils, moisture, and the coin itself.

In the case of "brown patina", be very, very careful. that is toning that is probably just above the bronze -- the substances that form first after a coin is minted, such as copper sulfides, are brown or black and it is only later that the green stuff starts to form. If you are hitting brown, you are very, very close to the metal of the coin.

My personal experience is that when coins have such varied surfaces, mechanical cleaning is the only way to go. Otherwise, any chemical treatment, and DW is a chemical treatment, affects all the parts of the coin equally, which is not what you want -- you want to focus on specific areas, I would think.

Mark

[Johnny]

Thanks Mark and sorry for the delay in reply