A similar entry appears in the Wheel of Time Companion confirming the information available in the main story arc.
Author: Toral Delvar
The Illuminators were a guild that made fireworks, a secret they guarded closely. At the start of the series, there were two chapter houses, one in Cairhien and the original in Tanchico. The Cairhien house burned down while Rand was escaping Trollocs (TGH, Ch. 27) and the Tanchico house was destroyed by the Seanchan when the Illuminators there refused them entrance (KoD, Ch. 8). Illuminators were said to kill intruders (TGH, Ch. 27). Illuminators are not allowed to sell the secrets of the guild, and people thrown out of the guild are not allowed to sell fireworks (TDR, Ch. 40). The Illuminators were completely ruthless in protecting their secret, including telling tales such as that exposure to air could sometimes makes the substances inside fireworks explode without fire, and even more violently than fire did, in order to discourage close examination (Robert Jordan Question of the Week, week 18).
The guild house in Tanchico closes its doors after Tanchico falls to the Seanchan (TFoH, Ch. 17). Later, the Seanchan demand entry and are refused, leading to a fight in which an explosion occurs. As a result of this, the Seanchan make all the Illuminators they can find da'covale (WH, Ch. 15).
The Cairhienin chapter house was situated outside the city, on one of the hills about a mile away, surrounded by a wall twice as high as an Ogier with buildings inside. Inside, there are long, windowless buildings and a pathway leading up the hill to a flat courtyard at the top. The leaders, at least, are from the Chapterhouse in Tanchico and given the secrecy of the guild, it is unlikely that any of the people there were Cairhienin (TGH, Ch. 27). The Chapterhouse was nearly destroyed when Loial accidentally knocked some fireworks over and they caught fire from the shock (TGH, Ch. 27). These were meant for a display for Galldrian and Aludra was blamed for this and forced out of the guild (TDR, Ch. 40). The Chapterhouse was abandoned after this.
Fireworks always come with a warning that opening one could cause it to go off. For most villages, they are too expensive for anyone to do that.
There are a variety of fireworks, from simple ones that just make a noise, to large extravagant rockets (TDR, Ch. 40).
Mat cuts one open and when it doesn't look interesting, throws the contents into a fire, where they explode (TDR, Ch. 44).
Mat ties a bunch together when he is breaking into the Stone, with the aim of creating a large noise as a distraction, but the resulting explosion turns a small arrowslit into a hole large enough for a man (TDR, Ch. 54).
After the destruction of the guild, Aludra begins to plot revenge against the Seanchan. The way she intends this is by using fireworks as weapons, something that has not been done previously. She intends to use bronze lofting tubes, which she will call dragons, to fire what she calls dragons eggs up to two miles (KoD, Ch. 8). Mat immediately sees the possibility of this, but also seizes the opportunity to make use of the explosive powder when fighting the Seanchan who are after Tuon, using slings to fire shrapnel type weapons at the attackers (KoD, Ch. 37).
“I get these strange feelings. Almost as if something were going to happen. Something...momentous; that's the word. It's like knowing there'll be fireworks for Sunday” (Mat; The Shadow Rising, Chapter 4).
“So long as one Illuminator lives, the Guild, it lives too, and me, I still live!” (Aludra to Mat; Winter's Heart, Chapter 15).