Dusky and delicate are key the words. Potter's Pink is a very soft colour which is either warm or cold depending on context. Whichever side of neutral it appears, it is a colour born of the shadows. There are two variants, a lighter, brighter and more luminous version and a softer, duller and duskier version (see inside the caps of the tubes in the picture to see the difference in mass tone). As an oil paint (Pip Seymour's - looks like the dark version), it has a low tinting power and is semi-tranparent. In water-colour (W&N, looks like the bright version) it is quite granular and more intense - almost a rose rather than a pink. According to two pigment suppliers, Kremer and Rublev, it is safe to use in any medium but according to Cornelissen it is only recommended for aqueous media. It produces incredibly delicate mixes and is beautiful when used as a glaze or under another glaze. As you would expect of a colour with its origins in ceramics, it is lightfast and, when used with the right binder, very tough.
Sometimes known as Pinkcolour, Tin Pink or, in Germany, Nelkenfarbe (Carnation colour), Potter's Pink has its modern English name for a reason; it was invented by an unknown potter in Staffordshire late in the 18th century. It was one of the first "modern" pigments and, just like a huge amount of modern synthetic and stable colours, it is a metallic oxide. It has always primarily been a pigment for ceramics but Winsor & Newton introduced it as a water-colour under the Pinkcolour name in the 19th century. It was the first stable pink available in this country, far pinker than local earths and without the treacherousness of Madders.
As with so many of the older colours it fell out of favour as brighter, more powerful and cheaper alternatives were discovered. Currently it is available as a watercolour from Daniel Smith, Rublev, Pip Seymour and Winsor & Newton, as oil paint from Pip Seymour, as pigment from Kremer, Rublev and Cornelissen and as a pigment in an aqueous dispersion from Rublev so there are signs of a revival, especially as a watercolour pigment. If I've missed a manufacturer, please let me know via the comments.
I have been using Potter's Pink extensively in oils (Pip Seymour's). I find the mixing power to be low so real care has to be taken when selecting colours to mix it with; many newer colours are virulent in mixes and will simply obliterate it. As a result I tend to use it almost unmixed, either as a delicate glaze or as a gentle block of colour.
The clouds here are built from layers of Davy's Grey, Charcoal Grey, Cobalt Blue and Lemon Yellow (PY31 not the more common PY3) over a bright white gesso. Other parts of the sky are areas of Cobalt Blue, Cerulean, Zinc White and Flake White. Parts of the clouds have then been given an irregular barely-there glaze in Potter's Pink for warmth and richness. Its warmth has largely neutralised the cold grey but because it is applied unevenly and over many colours it gives a pulsating life to the clouds and helps them change colour with the light. There is also a gesture of more thickly applied Potter's Pink to help define the cloud and bring out the pinkness elsewhere.
Here is a painting with more widespread use of the colour. At the edges of picture it is over cold, dark areas. In the centre it is applied with varied opacity over Cadmium Yellow Deep. Towards the bottom right it is mixed with white. Elsewhere there is a very light scumbling, but it doesn't show so well at this size. It shows the ease with which the paint can mixed optically to make a wide range of glowing but delicate colours.
I find there to be a real lack of subtlety in much modern painting and I think this is due in part to contemporary trends in materials. In paint manufacturers' scramble for pigment load, intensity and purity of colour at one end of the market and a combination of brightness and economy at the other, colours have been getting brighter, brasher and more garish and the more delicate, understated colours have been left behind. As anyone who was fortunate enough to see the Veronese exhibition at the National Gallery last year will know, a skilled painter can make less intense colours sing out as brightly as one could want through a mixture of careful juxtapositions and the use of glazes. When this is done, the resulting painting can be bright and colourful without becoming garish. The same painting made from modern "sledgehammer" colours would be inescapably garish. By the same token, if an artist wants a subdued or delicate painting - maybe for a portrait, a flower or an overcast day - starting from a modern palette of cadmiums, azos and pthalos is making life un-necessarily difficult. Artists benefit from the bright, intense palette of today but I strongly urge them not to discount the older, more delicate colours. Potter's Pink is as useful and practical an example as any.