Hydrated Chromium Oxide Green
Transparent Chromium Oxide
hydrous chromium sesquioxide
Guignet’s Green
An enchanting deep Emerald green with transparency. This lovely color makes excellent glazes as well as interesting mixes which can actually go quite bluish in tints. Debate rages as to whether phthalo green (a similar color) can replace the historical viridian, and we have found the answer to be not completely.

Old Holland Viridian Deep oil paint, made with PG18
Some painters prefer Viridian to Phthalo Green PG7 as it is gentler in many respects. Though both are transparent the two have slightly different qualities. When mixing colors that are just shy of highest chroma (which happens a lot in realistic painting) Viridian is a much more straightforward green to use. Phthalo can be used, but may take another pigment or two to counterbalance it in order to achieve a similar effect. Viridian is often paired with cadmium in cadmium green mixes, probably due to the copper in Phthalo.

Old Holland Viridian Green Deep, pigment PG18
One interesting quirk we've found is that some brands of viridian oil paint actually seem to shift in appearance when dried. Out of the tube they may look almost indistinguishable from phthalo green, however after drying the two may appear different.

Michael Harding Viridian, made with PG18
Viridian has a very high oil content when made into paint, which may be important to keep in mind if painting in layers.

Williamsburg Viridian, made with PG18
In the Artist's Guide to Health and Safety Monona Rossol has information on working with pigments containing Chrome, however in her latest work she distinguishes that this color has Chrome III.

Vintage Bocour Dry Pigment, Viridian Green PG18
On a rather alarming note, we've noticed that Viridian pigment is becoming harder to find in paints. Perhaps due to its cost, in some corporate paint brands, such as Winsor and Newton, Viridian has become rare. That's too bad, as it is a lovely pigment with charms all its own.

Kremer Pigments Viridian Green, PG18
PG18 pigment data from David G. Myers, The Color of Art Pigment Database, Artiscreation.com,
Spurgeon, Tad. Living Craft: A Painter's Process. Mt. Airy, Philadelphia, PA: Zoetrope, 2018. Newer version available here: https://www.thomaskitts.com/page/36804/tad-spurgeons-living-craft,
Information about PG18 from Bruce MacEvoy, Handprint Guide to Watercolors, General information about this class of pigments from Handprint,
Douma, Michael (Accessed June 2026). Viridian https://www.webexhibits.org/pigments/indiv/history/viridian.html. Web Exhibits, Pigments through the Ages,
Rossol, Monona. The Artist's Complete Health and Safety Guide. New York, NY : Allworth Press, 2001. The book is rather dated, updated information is available from her website.
Excellent
In Golden’s lightfastness testing in oils, this pigment performed well. There were a few instances where it slid to ASTM II (very good) such as in Flake White in linseed oil, as well as in pure zinc white. Overall it performed at ASTM I (excellent).
Transparent
Potential Hazard, Use more caution
Artiscreation assigns a rating between lower concern and possibly hazardous (A/B rating). In the Artist's Guide to Health and Safety Monona Rossol has information on working with pigments containing Chrome, however in her latest work she distinguishes that this color has Chrome III. The NPIRI mentions Boron Oxide as well.
Slow, may contain driers
Spurgeon writes this is, "not the best drier."\Some paintmakers add driers and reduce the dry time to 1-2 days. Driers can introduce their own problems later down the road.
Varies from Medium to Very High
Some sources say very high. Mayer assigned it to the Very High category with a score of 233 (one of the highest). By weight, Artiscreation lists a range of approximately 90g/100g of oil, but your pigment may have different requirements. Weight ratios are a more dialed-in way to go about paintmaking, but volume ratios are more helpful for visualizing relative amounts, since pigments vary in weight.
Hydrated chromium(III) oxide
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