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antonio
11-27-2001, 08:33 PM
I've been hearing a lot about these new pigments.
The transparent iron oxides. Can somebody please educate me about them.
Are they similar to the regular Mars pigments?
Are there any additives ? Are they permanent and lightfast ?
What makes them transparent?
Finally, what is Blue Ochre ? or Blue Oxide ?
Is it a synthetic iron pigment similar to those above?
Thanks for the info in advance.

Einion
11-28-2001, 12:42 AM
The transparent iron oxides are exactly what the name suggests. If you check the labels of the paints they should list the pigment as something like Synthetic Iron Oxides with numbers like PY42 and PR101. This is no real help unfortunately as these same numbers are used for Mars Yellow and various red earths (both natural and synthetic) but in no other respects are they similar as they do not share any of the classic mars characteristics like opacity, tinting strength and matt drying although they should still be reasonably fast dryers in oils.

They should be very transparent indeed - much more than a typical Raw Sienna for example. Like in many transparent pigments the transparency is related to the shape and size of the pigment particles.

They are not in fact new, what they really are is a rediscovery by some manufacturers of a very old and venerable class of natural earths that largely fell by the wayside in modern paint ranges except for the commonplace Raw and Burnt Sienna. They are valued for glazing obviously and since this is a critical test of lightfastness it is a shame they are not quite as stable as their natural counterparts but in oils they should still be ASTM I or II.

Blue Ochre may be simply a commercial name, check the label or product literature to see what pigments are listed. At a guess it might be a violet form of PR101 like Venetian Red or Mars Violet.

The name Blue Oxide is usually associated with various oxides of nickel, cobalt & titanium, essentially a different form of PG50, Light Oxide Green. It is typically a mid-valued, transparent, slightly neutral blue-grey or blue-green with very weak tinting strength.

Hope this helps,
Einion

antonio
11-28-2001, 09:19 AM
Thanks for the info. Sorry if I didn't explain in detail. I've been buying dry pigments and the list doesn't give details as to the chemical composition of the colors, unfortunately.
Normally I buy my pigments from Kremer , Doak or Guerra.
I happened to see samples of this Blue Ochre and/or Blue Iron Oxide which appeared to be the same pigment.
I overheard someone mention iron/phosporus ?
I want to know if it's a permanent/inorganic lightfast pigment before i use it.
So i was curious as I had never heard of it before. I was in a rush and never got to ask about them. I will next time i'm at a pigment supply house.
Again you've really helped. Thank you.

sarkana
11-28-2001, 09:21 AM
both blue ochre and transparent blue oxide are lightfast.

blue ochre is pulverised vivianite, a naturally occuring mineral. it is very opaque in oil. the color of blue ochre is a deep dark blue with a touch of green, like a black stone at the bottom of a swimming pool.

transparent blue oxide is a synthetic iron oxide that has an additional additive (like tin? not sure, i will check) in the manufacturing process. it's a transparent blackish blue, similar to prussian or milori blue but even less blue.

if you haven't tried either transparent red oxide or transparent yellow oxide, you ought to give them a go. i recently added those colors to my palette and am really enjoying the effects.