"Pure" blue?

I got involved - briefly: I soon pulled out again - in a discussion on Facebook about pure blue.  Some actually addressed the question, others just parroted a list of their favourite blues (which actually might have been a more intelligent response).  My two penn'orth was that I don't think there IS a pure blue, and if there were, it wouldn't be of any help to us as painters.  Others returned silly replies that you would have expected: lapis lazuli (oh for Heaven's sake!), cyan, Prussian, Pthalo, Ultramarine, Cobalt (slightly more sensible), Cerulean/Coeruleum; no one mentioned Manganese, at least last time I looked. Now, I've gazed into the sky and asked myself how, on earth, or over the earth, could I replicate that colour; and I've seen, and painted, any number of pictures in which the blue of the sky is a symbol, not any real attempt to replicate it, because - well, however great you may be, I just don't think you can. Now, to cut a long diatribe short - I don't think there is such a thing as a pure blue, and if there were, the sky doesn't represent it.  I believe we're all using a template colour, as it were, to represent "sky blue", and it looks about right, or can do, and so we accept it.  I wish we could represent the REAL sky blue, the real golds and oranges of sunset and sunrise.  I know I can't do it - I've tried, but I can't.  But if anyone here thinks they can, please say so - and provide your workings.   I think the questioner seeking a pure blue is pursuing a chimera  - I have seen the most recent development of a blue, and it's very beautiful - but incorporating it into a painting....?  And is it a "pure blue"?  And COULD it be?   We veer off into science here - I can't go far in that direction.  But - I should be interested in others' views, all the same.  

What Denise is describing is what just about all of us have gone through in trying to mix the colours of nature - it's absolutely worth doing, but you do have to remember that paint is man-made, the colours of nature are made by - whatever you choose to believe makes them, but certainly not humankind.  The science is available from Michael Wilcox's School of Colour, for those with an interest in that side of it - my interest is limited to what works in a painting, but there's a range of information for the scientifically literate; Wilcox's gift to painters is that he offers both the practical implementation of scientific evidence and information, and the pure science itself. Now, I am NO authority on this - but as I remember, Process Blue is just a neutral blue that will lend itself to colour mixing as Cyan succeeds in mixing with neutral red, yellow, and black to produce colour plates.  It's not a pure blue, any more than the other colours are pure - they're just as free from being drawn towards other colours as possible.  A painter will use Ultramarine, a red leaning blue; Cadmium red, an orange leaning red, or Alizarin Crimson or Magenta, which lean towards (i.e. contain within them) a blue.  Wilcox points out that if we did have pure colours to work with as painters - they wouldn't work at all.   If we had just the colours of printers' ink to work with, plus white, could we paint with them?  First, you'd need to know exactly what's in those colours - because their exact equivalents aren't available in tubes of paint - ideally you'd need to know, but you could make an approximation, and yes, it would probably work, at the cost of creating considerable frustration because of the lack of subtlety.  It might be a useful intellectual exercise, but I wouldn't (and won't) bother with it because it wouldn't really be practically useful.  Painting is about much, much more than achieving "pure" colour - if you have a basic palette, especially the split primary system, you'll have all the colours you really need; and the rest as helpful extras - e.g. I discovered Cobalt Teal recently: a beautiful colour, much used by the New Zealand artist Andrew Tischler.  But I don't need it, any more than he does.  It's like the cream on your raspberries - inessential, but luxurious (just not all the time). The pleasure and experiment lies in what Denise is doing, in short; and any search for pure colours is likely to lead nowhere: in response to Alan, I can say with some certaintly that Process Blue isn't pure blue: but I'd need Michael Wilcox here to explain why it isn't.....