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antonio
12-27-2001, 07:58 PM
Somebody help !
I think i'm losing my mind. I've been trying, so far unsuccessfully, to get any reliable info on a pigment called Blue Ochre.
I've read lots of art books, used the web and asked several dry pigment suppliers and have come up empty.
What pigment number is blue ochre ?
PB ___ ? Does it exist ? or is this pigment just a proprietary name for Prussian, Milori, Indigo or other blue?
I have been told that it's iron phosphate (a synthetic) and/ or vivanite.
Does anyone have legitimate info on the chemical composition of this pigment and if it's lightfast/permanent?
Thanks in advance........antonio

lori
12-29-2001, 04:08 AM
hi antonio..

thats a tough one.

as far asi can figure out, it would be PB27, the same as the prussian family. the reason that i would say that is that both compounds are made up of a ferric base. ochre is ferric oxide of iron and PB27 is ferricferrocyanide which is an inorganic synthetic.

it depends on how they are treated that would change the pigment from a midori to a paris to an iron blue (or chinese or bronze blue for that matter).

point being is that i would treat it the same way that i would treat a PB27.

lightfastness is: ASTM D4302 I (one)
average drying
hard, fairly flexible

chemical description:

ferric ammonium ferrocyanide precipitated by reacting a ferrocyanide with a sulfate and then a (bi) chromate. alterations in processing and after-treatments result in many speciality grades.*

*which is where you probably found a blue ochre in the first place.

call it chemical semantics...

hope that helped.

Patrick1
12-29-2001, 04:29 AM
This is a rare colour. Here's what I found:

http://www.kremer-pigmente.com/englisch/10400e.htm

I could be wrong, but as an inorganic earth colour I would expect it to be very lightfast.

antonio
12-29-2001, 12:03 PM
Originally posted by lori

thats a tough one.
as far asi can figure out, it would be PB27, the same as the prussian family. the reason that i would say that is that both compounds are made up of a ferric base. ochre is ferric oxide of iron and PB27 is ferricferrocyanide which is an inorganic synthetic.

point being is that i would treat it the same way that i would treat a PB27.

call it chemical semantics...
hope that helped.

thanks lori....... I think I'm going to take your advice and consider it some form of Prussian Blue PB 27 , unless I get other substantial info. .......antonio