Mineral oil does not have many solvents, so I have been testing mixtures of mineral oil from the drugstore (AKA baby oil) with various popular brands of train smoke fluids. I have not found a train smoke fluid that does not dissolve in drugstore mineral oil, so I conclude all are of a mineral oil base.
My experiments with various train smoke fluids and drugstore mineral oil indicate that the rate of smoke production and the smoke's density are a function of the viscosity of the fluid. I determined this by comparing the smoke production of straight mineral oil from the drugstore, to various non-diluted popular train smoke fluids, and from mixtures of equal amounts of both in the same MTH Rail King steam engine.
The lower viscosity oils produce denser smoke more rapidly than higher viscosity oil. Mineral oil from the drugstore (AKA baby oil) has a higher viscosity than all of the train smoke fluids, so by itself, drugstore oil is smokes but marginally.
I find that the higher viscosity drugstore mineral oil lasts longer, so I use an equal mixture of drugstore oil with train smoke fluid for a reasonable smoke density and longevity.
Cost is also a factor. Train Smoke fluids cost $3 to $4 per fluid ounce, whereas drugstore oil is much much less expensive. So mixing the two increase longevity and reduces cost. I us a lot of smoke fluid.
Having used the straight drugstore mineral oil and various mixtures over the last 3 years, the smoke units on my locomotives have not failed because of any of the fluids I use. However from my experience, the fastest two ways to ruin a smoke unit are to run it dry and to overfill it to the point the fluid gets into the fan motor.
Candle oil scents do not dissolve in mineral oil, so forget about using them.
