"subtle process" is a perfectly valid phrase in written English.
You can use it to describe something that happens slowly or gradually, without being obvious or noticeable. For example, "The subtle process of erosion slowly eroded the cliffside until it eventually collapsed."
"This is a very subtle process".
Falling in love with Buffy The Vampire Slayer is a subtle process.
Pacino's "nibbling away at a character," according to Barry Levinson, is a subtle process.
Jones – understandably given the book's subtitle – treats class hatred as a one-way street, rather than a collusive, often subtle, process which demeans everyone.
Editing an episode of "Curb" is an excruciatingly subtle process, in which decisions about narrative are made frame by frame — each frame representing one-thirtieth of a second of actual airtime.
For the most part, up high in the notches and ridges, this is accomplished by oozes and trickles, seeps and springs, a gentle, subtle process with charms -- damp and boggy charms -- of its own.
Now the task is to unravel the more subtle processes that have governed our evolution and development as human beings.
We have sensors and autonomous underwater vehicles to measure the subtle processes that drive ocean currents and govern the oceans' exchange of heat and chemicals with the atmosphere.
But the $145 million NASA satellite, called MAP, that will be launched this summer is intended to collect hints of subtle processes that took place during that epoch.
A central aim of this arrangement is to avoid the subtle processes of domination by small factions and dogmatic leaders that have undermined many emerging social movements.
Tabulation techniques can provide a detailed chemistry description which is needed to represent the subtle processes that occur during ignition.
