Erithi culture is an Official GemStone IV Document, and it is protected from editing.
Hand Gesture: An erithi with an empty hand held still and palm held outwards means they have no hostile intent. Why? The hand is empty (no weapon) and held still in such a position that no casting gestures could be made. Per the poetry log, the erithi NPCs during the Red Rot made this gesture frequently.
Both of these tidbits can be considered canon. Not all couples will use a wedding bowl, as not everyone would follow tradition (though most would). Some radicals hanging out over in these lands might even use a different material, but it certainly wouldn't be attributed the symbolic, traditional meanings by any usual erithi. The hand gesture could obviously be used in a ploy by an evil erithi too, a way to put someone at ease. So, don't relax just because someone does it!
Skyfire is an artform that encompasses storytelling punctuated with elaborate pictures made via a fire-cannon of gnomish derivation. Since erithi had contact with other races well before they let themselves be known, this doesn't mean it's a new artform, but could have been generations in the making. It also could have had its origins earlier with their own versions of simpler fireworks and the fire-cannon made it easier. Also, just because it is a released artform does not mean every erithi will enjoy it, consider it art, etc. In short, like the rest, it enhances but does not limit your roleplay choices.
It is obviously an art that can only be done at night when the skies are right for viewing.
Ilithelan says, "We much admired the fire cannons of the gnomes." Ilithelan says, "And asked them to supply us with one of their machines." Ilithelan says, "Once we acquired one, we put in some innovations of our own." Ilithelan says, "To create what we consider an Erithian artform." Ilithelan says, "Combining the spectacle of the fireworks with our own words." Ilithelan steps to the edge of the precipice and signals to someone below. She turns and faces the crowd. Ilithelan recites: "We are Erithi: Born of magic, rent from the skies, and suffused with the colors of this world." A flare arcs from the cannon with a resounding thunderclap that resounds through earth and bone. Brilliant, unsullied white as it begins its lazy arc through the heavens, the ball of light takes on hue and shape as its movement slows. Like an unfurling scroll, it spreads into a hazy and multicolored image: a small group of people in simple yet vivid-hued clothing hove amidst the stars. Their shining pates and tapered ears distinguish them as Erithi. The image lingers tenuously in the night before beginning to fade away. Ilithelan recites: "Whether created by the Grandfather, as some suggest, or wrought by nature's mystic warpings, we appeared in the distant reaches of the northeast. Across the narrow sea only the fallen Ashrim once tamed, we flourished." Another belching of light and sound erupts from the mouth of the cavern, causing pebbles to shower down the nearby mountainside. The flare elongates into the shape of a sunlit sea dotted with pale ships. The ships fade, and a landmass bubbles forth from the fiery waves, dotted with greenery and rolling mountains. Tiny settlements wink in and out of existence along the coast, disappearing almost as swiftly as they form.
I finally came across a log of the theatre mask event at HSN 2004 (and by finally, I finally realized that that was what that massive 400 page log was that someone sent me when I first became guru). I've skimmed it, and I wanted to share with you what you can consider "official" from that.
The NPC was Chelan, and rather than talk herself about theatre, she wanted to hear an outsider's view who claimed to have been studying it. A player character, Tierus, gave the talk on what he called shi'hadara. The NPC was guarded about her opinions, but did not jump up and down and scream "you are so far off you must have been smoking something" either. Therefore, I'm going to make it official that there is a theatre style that is at least similar to what was described, but I'm staying intentionally vague. I do have a more fleshed out document around this that I will be having reviewed and such, so we can tie up a loose end around something that might be confusing as far as officiality and such.
So, for this particular theatre style, the name itself isn't official, but speaking of elements in general covered during the talk would be fine. You are safe in assuming that there are many other variations of theatre that are popular among different groups of the erithi, so this one style is not the end all-be all, either. You can also consider it official that other styles of theatre utilize masks as well, based off Chelan's visit. Plus, like poetry, lots of symbolism can be read into the masks, and some make an art of it, and some might find it silly, while others profound.
In other words, plenty of leeway for your characters here!
One thing Chelan did which was really interesting was ask people to tell her one of their weaknesses or fears and let her design the mask for them based off that. She went on to say that this was a discipline of sorts. If you put your weakness or fear into the mask, and then put the mask on and play that part on the stage, you are removing it from yourself, because it is just a mask. Then afterwards, you remove the mask, and that part of yourself as well. In short, the theatre mask design (not to be confused with the masks described by Tierus in his talk) can be considered an art form as well as a philosophical one, should someone so choose.
Again, your character can take it or leave it, but it is there. You may consider "the Discipline of the Mask" to be something erithi. Obviously masks do not have to be designed with this in mind and they can hold other symbolism for the creator or wearer or none at all.
I found 4 examples of the masks in the log that I wanted to share, names have been removed. These are absolutely gorgeous, and the GM behind Chelan did a remarkable job. The only "error" is that the base is "an Erithian,festival,mask" where "erithi" would be more appropriate and "erithian" would be acceptable. However, I don't think we had standardized that you don't capitalize races at that point, so obviously it isn't an error really. Just remember if you have one made to lowercase it!
Female sylvan: examining an Erithian festival mask. Deep blue dyes cover the front of the fine silk mask so thoroughly that its original snow white hue is only visible from the inside and from a slight rim around the eyeholes. In the center of the brow, a brilliant star shimmers in silver and gold, and tiny sparks stream from that star to cascade over the temples and cheeks. Long lashes have been painted around the eyeholes in a fashion that suggests the eyes are gazing upward, and the mouth is contorted in a scream.
Unknown erithi: examining an Erithian festival mask. Dark-hued dyes cover the front of the fine silk mask so thoroughly that its original snow white hue is only visible from the inside and from a slight rim around the eyeholes. Dark violet veins curl over the brow and above the eyeholes before curving down to create twin nautilus shells on each of the mask's cheeks. Silver lines shape a set of uneven scales on the forehead, and a sword lies in each scale. The mouth of the mask is shimmering silver.
Female erithi: examining an Erithian festival mask. Half of the mask is snow white, but the other half is shadow grey, and the two sections are divided vertically. They are not truly halves, however, for the line runs to the left of the nose, allowing the shadowed section to encompass more than the white. The eyeholes are unnaturally wide and rimmed with black to make them appear wider, while the cheeks are stained brilliant red. Equally brilliant red, the mark of a whiplash curves over the right cheek.
Male aelotoi: examining an Erithian festival mask. Pale, slightly tinted dyes have been used to paint a pattern that resembles raindrops streaking over pale crystal upon the snow white silk mask. The only strong spot of color is a set of three dark red lines, which create the simple, stylized shape of a grinning fox's head with an open mouth. At the center of the mouth, just above the thin speaking-slit in the cloth, silver traceries suggest the shape of a kiramon perching on the fox's tongue.