The exact mechanism for a materialization is not known for certain, but I have been sent so many photos over the years that I am able to speculate that ghosts go through four stages as they materialize. It is important to keep in mind that ghosts do not progress through these four stages quickly, it sometimes takes weeks for a ghost to move from one stage to the next. I've determined the order for these stages by simply counting the number of photos that I receive for each stage. I assume that all ghosts start at stage one but then many lose the energy needed to finish the entire process. Therefore, I expect the most photos from stage one and then a decreasing number of photos for each of the remaining stages. If that is true, then the following is the most likely progression for a ghost from immaterial to corporeal.
An orb looks like a globe or ball on a photograph. Normally, an orb has some sort of visible internal structure, which is how I can differentiate orbs from simple dust particles. The purpose of an orb is to gather energy so the ghost can materialize and when guests on my tour start to get photos with a lot of orbs someone frequently complains that their battery is about dead since the orbs will drain the energy from that battery. Oddly, when the trolley leaves that immediate area those batteries tend to return to full strength. Because orbs gather energy, they are present throughout the entire materialization process and are needed for the ghost to move from one stage to the next. Orbs are very common in Tombstone and many of my guests can capture photos of orbs during my tour. Guests also frequently send me photos of orbs that they took during their stay in Tombstone though not while they were on my tour. The accompanying photograph shows several orbs at the intersection of 4th and Allen Streets, where the Visitor's Center is located. Notice how the larger orbs display an internal structure.
A plasma looks like smoke or fog on a photograph. There are always orbs mixed in with the plasma since the ghost continues to absorb the massive amounts of energy it needs to move to the next stage. When it is young and immature, a plasma has no form and resembles a fog bank rolling in. However, as the orbs gather energy, a plasma will begin to consolidate into a "fuzzy blob" that swirls around like smoke but, unlike smoke, it swirls very slowly. From time-to-time, a body part, like a hand or face, may appear in the plasma. That part will only stay for a short time and will eventually be engulfed and disappear. In the accompanying photo, a plasma is visible near the corner of 2nd and Toughnut Streets, where John Heath was lynched. This is an immature plasma that has no shape and looks something like white smoke on the ground.
A vortex looks like a streak of light on a photograph and there is normally a visible orb or two mixed in with it. A vortex can be differentiated from simple camera movement because other items in the photo are in sharper focus while the vortex is blurrier. As the energy is gathered, the vortex becomes longer and more sharply defined. A vortex starts as a nebulous plasma, but as the energy increases the vortex begins to coalesce into a sharp streak of light. The vortex in the accompanying photo is at Boothill Graveyard and appears as a streak of light on the ground crossing over several graves. This vortex is rather sharp, so it is likely mature. If the energy level remains adequate, a vortex will evolve into the next stage, an apparition.
An apparition takes many forms on a photograph, but it normally has an identifiable human, or even animal, shape. We normally think of ghosts as white, but an apparition can be in muted colors, shades of gray, or even a shadow man. Because this stage requires so much spectral energy, apparitions do not often appear for a long period of time; they tend to be present for only a few minutes and then revert to stage three or vanish altogether. The accompanying photograph shows a man looking out of the top right pane of a window at the courthouse. The ghost is rather hard to see, but that is the way ghosts are. Perhaps this ghost is near the end of its visible time, so it is a bit weaker.