IATSE in Seattle, which is a labor union for stage employees and film crews. Certain jobs in the trade still carry the age old tradition of categorizing the experience level of the worker.
A new worker has no title. They might be referred to as a skilled laborer, but otherwise they would have no title. Once they gain some experience they can become an Apprentice. Historically an Apprentice would have to be tied to a particular Master, but currently that is not necessarily true. Once an Apprentice has learned enough to become proficient at a craft he can become a Journeyman. One can spend years as a Journeyman before ever being considered a Master.
When I would work for the Seattle Opera, I would often work for the Master Carpenter. At the Paramount Theater, I often worked for the Master Electrician. These titles are a bit misleading because in the theater a carpenter actually just builds the sets and does scene changes, while an electrician deals with lighting. The point is, you cannot be considered a Master until you have years or even decades of experience in your craft.
You can read more about the Apprentice-Journeyman-Master model at the Wikipedia article.
The point as it relates to research for writers is that if you really want to dig deeply into a topic, there is no better research than seeking out a Master of the craft. A person who has spent their entire life perfecting their skill will posses such a depth of knowledge regarding the subject that it will boggle the mind.
That kind of first person source cannot be matched through reading, or even experiencing, something yourself. Jumping out of an airplane once, or even five times, does not make you an Airborne Ranger. There are nuances to such things that can only be understood through living them for a lifetime.
This is not the kind of thing many writers can manage to accomplish. I for one have never interviewed a Master regarding a topic that I wanted to write about, but I know the option exists. Potentially it could be extremely difficult and expensive to do, depending on what you need to know.
If you need to travel to Quantico to speak to the FBI behavioral science experts about profiling serial killers, and you live in California, you'll probably have to be a very successful writer to be able to afford it. However, if I really wanted to, I could probably find Master Blacksmith somewhere in the state of Georgia who I could meet and interview for no more than the price of gas and lunch. And probably beer. A lot of smiths seem to like dark beer.
It all depends on what you're looking for and how much detail you need. For WARRIOR-MONKS I don't think it's necessary. I've learned enough from books about forging a sword that I think I've created the scene in an authentically believable way (assuming you're willing to believe in a little magic). I don't really think there is anything so specific in my novel that it would require speaking to a Master to do it right.
Yet, I would love to one day write a story that did require the knowledge of a Master. If I did, there would be no better source than a person who had spent their life gaining a mastery of their skill, craft, trade or art.
Yes, that is the Osensei Morihei Ueshiba up there. Have a great weekend!