I am creating a long timing circuit using a CD4060. What technology cap is the most reliable to use in such a circuit? Also, what is the max clock value that you would recommend to sustain a fairly stable pulse (ie what is the longest pulse period and what value do he caps leak too much to be reliable).
Have you considered using a tiny microcontroller like one of the Microchip PICs ? The smallest ones are not bigger than a cap suitable for your application. They come with built-in RC oscillators, and with a few instructions you can make delays as long as you want replacing both your cap and the CD4060. If you want you can also run them off 32 kHz watch crystals, for improved accuracy.
There is a problem getting long intervals directly, since large value caps tend to be either electolytics, which are not very stable, or else they are physically large (and expensive). If you are sure you want to go this route, polystyrene is usually regarded as most stable. (Well, last I looked anyway; there may be some new technology that is better.) I think polypropylene is also pretty good.
But the better way to do this is digitally, as the other reply suggested. You don't really need a microcontroller, however, since you can use a high-frequency clock and count it down as low as you want. Since you are using a 4060 (14-stage counter) already, if the final stage is not slow enough, just cascade another 4060. If you don't need the full precision of a crystal, at least this way you can use a small precision capacitor like polystyrene, silver mica, or even NPO ceramic and get a pretty stable high-frequency oscillator.
Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis