Naphthol Scarlet Lake, Naphthol AS
PR188
Alternate Names
Naphthol AS BON Arylamide
PR188HF3S
Naphthol Red HF3S
Pigment Description
There may be two varieties of this pigment, as we have encountered lightfastness ratings for a regular PR188 and another one called PR188H3FS. The regular version seems to be slightly more lightfast. We love this color but it does not seem to be as lightfast as we'd wish. In watercolor this color has a fairly deep masstone which readily makes delicate, transparent, lilting washes of candy-chroma reds. Schmincke gives their version three out of five stars for lightfastness, which means it's lightfast but not the highest levels.
In regard to regular PR188, the term Naphthol AS gets applied to a handful of pigments, so this may refer to a really fabulous color which used to be quite popular in some smashing convenience pinks, which did not contain pigment data but simply read "naphthol as" without further information. If PR188 is the Napthol AS we've used, it is truly gorgeous, and we were loathe to retire it from our palettes. There are reports that it may fade in tints, and some consider a BWS 7 to be fine. Bruce MacEvoy's watercolor tests indicated that it was lightfast above an ASTM II, which is not too bad. Some sources show only moderate lightfastness in tints (BWS 6), which is too low for our purposes. PR188H3FS Is listed as Naphthol Red AS, and it has a separate lightfastness in watercolor of ASTM III.
Resources
PR188 pigment data from David G. Myers, The Color of Art Pigment Database, Artiscreation.com
Information about PR188 from Bruce MacEvoy, Handprint Guide to Watercolors, General information about this class of pigments from Handprint,
Stats
Lightfastness
Very Good but not Excellent
Lightfastness may only be moderate in tints. PR188 is often said to be Excellent in Oils and Acrylic but we would question this a bit. Its results are sometimes listed as Very Good in Watercolor. The ASTM II in watercolor is of interest. Bruce MacEvoy found some brands which were slightly better than others, however he recommends more lightfast pigments instead. Some tests of PR188 show fading in tints even indoors, and Artiscreation reports some darkening and/or fading.
Transparency
Varies, Semi-Opaque
Can vary anywhere from transparent to opaque formulations in oil, Semi-Transparent in watercolor
Toxicity
Hazard, Use more caution
Artiscreation rates this as a B, so there are precautions that are needed. Always consult the SDS as well as third party expert sources. In general, treat all pigments and paints with studio safety protocols.
Dry Time
Varies
Some brands make oils that dry in 2 days while others list this as moderate or even as Very Slow. The wide range makes one suspect the use of driers in the faster varieties.
Particle Size
Fine
Chemical Name
Monoazo, 3-hydroxy-2-naphthanilide, AS
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