View Full Version : Colour variation and application

10-02-2002, 04:16 PM
A couple of points raised by a new member I thought were worth discussing in a new thread:

Originally posted by Mickey Lee
I work with acrylics, which are chemically made. Each are given a specific pigment number. So why is there such a big difference between one brand to the next - same name, such as Raw Umber.
An important question, unfortunately there is no simple answer to it. Take a classic modern synthetic pigment, PV19. This number can refer to the a number of forms of the same quinacridone pigment, resulting in red, rose and violet hues. Hopefully the name the manufacturer chooses to associate with the CIN helps to clarify what you might be buying but all too often they are no help at all and the only option is to look for a hand-painted colour chart or to open the tube and check for yourself (which is obviously frowned upon!) Even knowing which type you have can at times do little to pin a colour down, especially if you have a very specific liking or requirement - until you have actually handled the paint and mixed it with other colours you're familiar with, you really can't get a good appreciation for the individual character of what is in the tube. The gamma form of PV19* for instance can vary from a medium dark-valued crimson to an almost mid-red of lighter value; undercolour and tint differences will also be pronounced. Then take into account variation in pigment load and other characteristics from make to make and you can have two colours that you might expect to be almost the same but in reality can be very different indeed.

Earth pigments like your example are even harder to pin down. The sole pigment designation PBr7 is a very vague definition for natural earths of incredibly varied character - from light siennas to dark burnt umbers. What has made this even worse of late is that supplies of genuine earth pigments have begun to be exhausted and manufacturers are permitted to still use the PBr7 designation for synthetic earths used in place of the real thing. Now these can be very good pigments, but all too often they are not quite what one was expecting, especially if you are used to how a colour "should" be. So, even when Raw Umber** was solely made from mined earth pigments the colour could vary in many respects: yellowish, lighter-valued and higher in chroma from one maker, darker, slightly greenish and more grey from another; very transparent from one and semi-opaque from others.

Originally posted by Mickey Lee
A question I would like to ask is about the value/use of transparent/opaque colours. How do these work with colour mixing/schemes?
Another very good question but again with a very complex answer. This has been touched upon in previous discussions in this forum if you would like to search back for them.

Take a single hue, say a high-chroma red. This same position can be filled by Cadmium Red Medium and a number of synthetic organic pigments, let's choose Naphthol Red, PR112***. In masstone the colours might look very close but one is opaque, the other quite transparent; the former has a subdued tint while the latter's is much brighter. In mixing with another colour the results will of course vary in opacity, a fairly important consideration in and of itself, but because of variations in the particular nature of each colour the hue also varies far more than one might expect. The undercolour of PR112 from W&N is surprisingly crimson for a red with this masstone for example (much more so than Golden's appears to be) while PR108 has a consistent orange-biased undercolour; so at first glance they look similar but in use they are as different as chalk and cheese.

This is one of the primary reasons (no pun intended) I think most painters should select their colours carefully to tailor their palette to their requirements - don't buy a paint simply because you like its colour but consider its other attributes too. Obviously there is a limit in certain instances to how much one can do this - there are no opaque pigments that are even close to Phthalo Green BS for instance - but many oil and acrylic painters would be better served by a palette almost entirely of opaque colours while watercolourists could use similar hues but almost all transparent pigments.


* Quinacridone Red from Golden, Permanent Rose from W&N Finity, Quinacridone Red from Tri-Art, Quinacridone Rose from M. Graham.
** Compare Raw Umber from W&N Finity and Golden, both made with PBr7 but very different, with that from Maimeri Brera, a blend of PBk11, PY42 and PR101.
*** Cadmium Red Medium Hue from W&N Galeria, Naphthol Red Light from Golden, Naphthol Red from M. Graham, Naphthol Red Light from Tri-Art.