Highlight: Manganese Blue

It's a well-known fact that manganese blue is, or at least almost is, an extinct species of pigment.

At the time of this writing, it's still available in dry pigment form from Cornelissen Pigments*, and in watercolor tube by manufacturer Old Holland* at some online retailers and in pan form from the boutique paint maker Pen Holder Arts*(at least occasionally).

Side by side swatch of boutique vs large manufacturer

For interest's sake I got my hands on both available brands of genuine manganese blue and compared them. I found they were similar except for pigment load, that is to say that you need far more of Old Holland's manganese blue paint to approach what Penholder Art's can achieve with so much less. Another point of interest is that Penholder's is a pan paint but much more easily wet and disolved in water than the tube paint from Old Holland, which struck me a touch odd.

As a side note: I recently discovered that one online retailer, Jackson's*, seemed to no longer carry the PB33-only variety of Old Holland's, replacing it with a Manganese Blue Extra(a multi-pigment paint). After communicating with interested parties on the subject, I found that Old Holland ran out of PB33 more than a year ago, and consequently, remaining retail stock is running out.

Though rare, this pigment is widely regarded for its hue, granulation, and low tinting characteristics. Handprint's author said of it "This crystalline synthetic inorganic pigment, a near perfect cyan hue, imparts a lyrically coarse texture even after extensive milling. Though never a popular paint, I feel this is of the loveliest blue pigments ever used in watercolors: it imparts a unique poetry to sky, water or landscape greens when used in diluted mixtures that put its granulation on display. "

4x6in Plein air piece from Union Street Railroad Bridge in Salem, OR - Steven Drenning Jr

The above piece illustrates PB33 in all it's glory. Used singularly and only in the sky here, you can see it's lovely granular quality starkly contrasting the quite similarly hued but non-granulating PB17 of Holbein's Irodori Antique Turquoise in the water below. 

*links may break