The exact mechanism for materialization is not known for sure. However, I have been sent so many photos that I can speculate that ghosts go through four stages as they materialize. It is essential 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 have determined the order for these stages by counting the number of photos I receive for each stage. I assume that all ghosts start at stage one, but 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.
Orbs
An orb looks like a globe or ball in a photograph. Usually, an orb has a 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 many orbs, someone frequently complains that their battery is about dead since the orbs will drain the energy from that battery. When the tour leaves that immediate area, 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 they took during their stay in Tombstone, though not while they were on my tour. The accompanying photograph shows several orbs at the 4th and Allen Streets intersection, where the Visitor's Center is located. Notice how the orbs display an internal structure.
Plasma
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 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. A body part, like a hand or face, may appear in the plasma from time to time. That part will only stay for a short time and will eventually be engulfed and disappear. A plasma is visible near the corner of 2nd and Toughnut Streets in the accompanying photo, where John Heath was lynched. This immature plasma has no shape and looks something like white smoke on the ground.
Vortex
A vortex looks like a streak of light on a photograph, and there is usually 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 sharp focus while the vortex is blurry. The vortex becomes longer and more sharply defined as energy is gathered. 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 an apparition.
Apparition
An apparition takes many forms in a photograph, but it usually has an identifiable human or animal shape. We 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 a great deal of spectral energy, apparitions do not often appear for an extended time; they tend to be present for only a few minutes and then revert to stage three or vanish entirely. 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 how ghosts are. Perhaps this ghost is near the end of its visible time, so it is weak.