Contrails are Ice Crystals
For the formation of contrails you need some special conditions in the atmosphere.
1 Temps below zero celcius.
2. A layer of super saturated (by water vapour) air.
3. Condensation nuleii, that is tiny particles, on which rain droplets or ice crystals form.
4. A jet or piston engine burning fuel to produce the small particles.
Con trails are a b#### nuisance if you are a fighter pilot not wanting the bad guys to see you so in such circumstances the met people can forecast the conning layer to allow the fighter jock to use to advantage.
The other stuff formed in very moist air when the air pressure and hence temperature is dropped around a fast moving or high g pulling aircraft is a mini cloud. Most of us call it 'ectoplasm"
Once again it is a nuisance if it forms around the canopy.
Condensation nucleii used in cloud seeding to produce rain is usually produced by the burning of a Silver Iodide solution.
Active seeding from ground burners is about to commence in the Australian Alps to increase precipitation.