Hi Sarah, a “ghost” as far as I am aware is of two natures. The first perhaps like the “Grey lady” type is really like a recording, which is triggered by some action. These can be seen by people who are not or do not have to be sensitive but it helps. The second is a manifestation that can take various forms and yes sometimes are seen as transparent the spirit manifesting can appear as they wish. If you have seen the film Ghost, which shows what I mean it helps the explanation. What you see there is true.
Within the first ten minutes of seeing the film the first time, I knew that it was written by a medium. I am told that it was the guy who plays the “nutter ghost” on the train, the one who teaches Sam to flick a bottle top. Just like in the film, they (we) can walk through doors etc because essentially not only are we, as energy, part of everything, every atom, but they are in another dimension where they are solid (for this purpose of explanation) and this world, to them, is not. Just like we unknowingly, are walking through theirs. So in a sense we are “ghosts” to them. Theirs is the true, eternal world, ours is but fleeting and a dream.
With Physical mediumship in the way that you mean it, the energy is supplied by the medium and sitters and ectoplasm is drawn from the medium which helps the spirit form a body. Again the body can take various forms and may be transparent or indeed invisible but still solid.
The spirit (depending on conditions and how it wants to present itself or again how much energy is there or can be used) may only form a hand, or a foot to tap the floor with and, in ideal conditions, fully form and walk around the room talking.
The spirit is solid to the touch, can appear cool but also surprisingly warm. Sometimes they allow you to touch them – it is only with their permission, and often they touch you, if they know you are open to it. They would never do anything to unsettle you.
What Maria experienced was, because of the love bond, and her own ability (Clairvoyance) and her openness to it, seeing her son. True clairvoyance means seeing a spirit (her son) outside the head, and as clear and solid as you see any other person. Of course, again, the spirit (her son) had a choice as to appear to her. He chose to appear as she remembered him. In reality not only would he have a new “body” the spirit one but depending on his age – we grow young if we are old, and grow up if we pass young, may well have matured or grown younger.
This is why often when spirit come (especially to the medium for readings) they show themselves as the client would remember them or as may be found in a picture if the client did not know them personally. This is the reason that “Granny” would serve no purpose in coming as a sprightly 25 year old and announce “I’m yer Gran!” it is confusing. Again they appear as they want to.
I have been in a room with ten or so mediums and a few (including myself) saw spirit and others didn’t. Spirit have complete control as to who, and how they show themselves. They can “cloak” themselves from vision or sensing from whoever they want. It is their choice, solely.
I hope this helps?
Light, always, Leo.