Do you think it would be a good idea to just substitute buying a transparent set of paints with buying opaque paints and then adding the reducer then? Seems like a real money saver.
You are better off buying transparents and you can make these opaque by adding a bit of opaque white or black/dark blue. Dru Blair calls this colour buffering, other call it 'capping' your colours. Be careful with adding darker colours as this can produce brown or muddy results. Better off using the darkest transparent and adding the smallest amount of white.
This would be a basic set, you can also add different coloured opaques to change colours and give the same capping effect.
To explain how buffering/capping works, when you spray transparents you can go from a very light tone to the darkest it produces with the more coats you apply. If you want to 'cap' that colour to a certain tone (below maximum) you add a bit of opaque white then it doesn't matter how many coats you apply the colour is 'capped' to that level.
Adding just the smallest ampitn of opaque paint removes the transparency so it all depends on what you want. Some use only opaques which gives you total control of your colours, some build up their tones using transparents and some use both by laying down the opaques then changing the tone where required with a little transparent to 'wash' over areas for example.
What all does the extender do?
Extenders are usually the natural clear base for the coloured paints, you add these to 'extend' your colour, basically it just makes more but thins out the pigment per volume without reducing viscosity.
With transparents it makes them even more transparent, with opaques it does the same but will never be a true transparent.
Reducers or thinners thin the paint making it less viscious, you can thin paint to make it more transparent but you are breking down the chemicals that help it bond the more you add, hence the need for extenders.
I use and sell E'tac so if you have any questions at all feel free to ask and I can help you with any specific attributes of this paint system..
I think you have the E'tac Condition-Air and Extend-Air mixed up, the Extend-Air is the base for the Private Stock line and the Condition-Air is the additive to help with flow and tip dry etc. It contains Glycerin also and from all accounts can be used with other water based paints as well
Only takes a 1-2 drops per oz bottled water to make a suitable thinner.