Components of the Costume
Nirrti's costume from the third season episode Fair Game breaks down into the following basic components: top, beading on the top, underskirt, overskirt, veil, headpiece, bracelets, belts and shoes.
There actually aren't very many good shots of her skirts. However, based on the scene when Carter has captured Nirrti and is leading her back into the conference room, I believe that the underskirt is a semi-transparent material, almost but not quite chiffon-like. For a second or two as Carter marches her forward, part of the underskirt flows to the side and you can just make out the shape of Carter's legs through the skirt material. Based on the theoretical thinness of such material, as well as well as the front view picture below, I think there are at least two layers to the underskirt. I have picked up a smoky lilac/blue material from Fabrics R Us for the underskirt. My initial mockup pattern didn't have enough fullness in the skirt. My next mockup will start with a full-circle skirt (McCalls 4569) and go down to a 3/4 circle skirt (simplicity 4883) if the former is too full. Thanks to kay_dee and ghilledhu for their tutorials and suggestions regarding skirt patterns!
It's hard to be sure, but I think the overskirt is a deep purple color. At first I thought that it was of a heavier, more opaque material than the underskirt, but in the scene at the end when Yu and Cronos march Nirrti up the ramp to the stargate, you can see the outline of a background object through the material as an edge flaps up. The final shot, as they walk up to and through the Stargate shows the overskirt material flowing more than in other shots, leading me to think it may even be something similar to the underskirt. From this scene and from the picture linked above, you can see that there is some sort of pattern on the skirt. I think it's a floral pattern. Whether or not I can find both the right weight and flow for the material and something with a floral pattern remains to be seen... I may end up having to use plain purple. If so, I believe I saw something at Fabrics R Us that would work. Another possibility is a purple floral material at the Cupertino JoAnn's. The down side here is price. ^^;; As for a pattern, I will likely start with the same pattern as the underskirt and draft out the diagonal cut myself.
Belt / Sash
Nirrti's belt / sash appears to be made from a few diffferent components. First, there is a sort of sash which follows the waistline of the skirt, coming together and hanging down several inches in the front. This material appears to be a purple base covered by a metallic pattern. The reference isn't good enough to get the details very well, but I'm guessing that a) the pattern is a paisley, and b) the metallic color is gold. I have purchased such a material from Hancock Fabrics and will post a picture of it sometime soon. The second component of her belt are what look to be two chains of rhinestones: one along the top of the sash and one somehow suspended a few inches above the skirt, parallel to it. The rhinestones look like a dark color. I've found something similar at Fabrics R Us, but I'm choking on the $10/yd cost (for real crystal of some sort). I don't need real crystal so I'm hoping to find/make something a bit cheaper. 'Cause really, I don't want to spend something like $20 on one small part of the belt. Gah. Finally, the third aspect of the belt is a gold circular disc outlined in the same rhrinestones, located just above the V of the waistline and bridging the gap between the two rows of rhinestones on the belt.
Reference picture: close-up cropped from above
Nirrti's top is a half-top with short sleeves. The neckline seems to go up a bit past the collarbone, following a close circular pattern around the neck. (In other words, not a lot of bare shoulder) I initially tried Simplicity 5359, altering the deep V neckline to add in what was needed, but I couldn't get that to work. I am currently looking to use either McCalls 4343 or Simplicity 4427, and simply cut off the top at the right height below the bust. The real top uses darts coming in diagonally from the side, from what I can tell, but I haven't been able to find a suitable top with that feature. Getting the top form fittng was more important to me, so I'm sacrificing accuracy in that regard and trying patterns with princess seams.
The material appears to be some sort of light lilac with sparkly and opalescent qualities. I haven't been able to find something to match this well. At the moment, my closest approximation is to take a very light and pale shiny base fabric and flatline it with a semi-transparent sparkly/opalescent material. I chose the latter to match the skirt material very well; unfortunately, when flatlined with the base fabric it takes on a lighter shade. A picture of the materials is here. The base material is shown alone on the right, the two materials overlayed on the left.
Beading on the top
The beading on Nirrti's top is a clever weapon designed to drive physicists insane. I am not kidding. First, there is no pattern to it. Physicists are trained to look for patterns and symetries, and this top doesn't have either. It's driving my physics-trained brain insane trying to figure out how to deal with something that looks like it should have a pattern or symetry - I keep looking for it, but it's just not there. The next crazy aspect is that the beading appears different in different shots. Colors change, density of beads appears different, and aspects that seems very aparent in some shots look to be totally missing in other shots. This makes attempts to copy the random pattern almost impossible.
So, to save my sanity, I'm just going to take some basic concepts and colors from the various reference shots, and incorporate them into my own design. It's all I can think of. The basic colors are green (large beads/stones), blue (large bead-stones), red (medium rhinestones?), deep orange (smaller rhinestones?), and black (thin tubular beads drawn in lines). The black appear to form a sort of vine and leaf pattern here and there. The green may or may not represent larger leaves (inconsistent); the red may or may not represent small flowers (inconsistent). There is also a finer vine and leave pattern visible when zooming in on the dvd that isn't aparent in any of the online pictures. I can't tell whether it is embroidery or lines of very small beads. Finally, there is a single row of black sequins around the bottom of each sleeve and a double row of them around the bottom of the top. I haven't completely settled on beads, but here are some that I am considering.
Reference pictures: see the pictures of above for the top
Reference photos: one
Nirrti did not wear a ribbon device with this costume, due to an aspect of the plotline, but damn it, I want one. Ribbon device research photos page