I have been doing some experimenting with NS aurora, trying to get different effects and am mostly ending up with brown... You may have seen this already on the Northstar Glass Borosilicate Colour Facebook group - I think forums can be more useful for this kind of thing (plus I had real difficulties finding any pics of things that were mostly aurora on its own).
Here's what I did so far.
First I made these beads. They all have a clear core. From left to right: aurora, encased in clear; aurora with clear frit, encased in clear; aurora on surface. They are mostly brown with a little dull pinky-red (slight hint of purple on one side of the fritty one). On the surface I got the rod colour. They went through my normal kiln schedule which has a striking segment at 621C (1150F) for 10 mins and anneals at 565C (1049F).
I looked up the Northstar newsletter about it:
http://www.northstarglass.com/newsletters/1.pdf
It says:
"For NS-47 Aurora it is also possible to get a full spectrum of colors depending on which flame is used as well as whether the piece is encased in clear or a color. To achieve vibrant blues, try working it in a highly oxidizing flame. To yield a green, work it in a neutral flame. To generate vibrant deep reds, work the piece in a neutral flame then reduce the piece when it is close to completion."
So, I'm on a Minor and 10lpm concentrator, so may not be able to get blues but I should at least be able to try for green, right?
So I tried turning my oxy up as high as I can get it and the propane down a little - gave me a hissing flame. I made these two beads. To get the lighter areas I had to really blast the surface and then allow to air cool for a long time. I still couldn't get the whole bead light. The light areas looked greenish before encasing and going in the kiln, but came out like this.
I then made an encased stringer, which looks a dull green with occasional pinker sections (see below).
The bead on the left went through the kiln and got a great deal darker. It's more purple than brown, but still pretty dark. The right bead is unannealed. I made it from the end of the rod I'd been using, so the blue streak is encased while the rest is plain aurora on the surface. Still really hard to strike, so the other side is all black, but there's a dark greenish section at the bottom of this side. Second pic shows the blue streak better.
You can see my encased rod and stringer here. (Rod also has a clear core). Nothing's come out of the kiln looking remotely like that.
I decided to do something a bit bigger next and with no mandrel in the way, so made a pair of scorpion claws.
One claw is solid aurora - still an awful lot of brown-black even for something with a much longer working time that was going in and out of the flame. I used a fairly high oxy flame but also enough propane to let me melt easily. For the second claw, I made a gather of aurora, encased it and then did all the shaping. It looked lighter before it went in the kiln, now it is weirdly salmony with other areas - a few dark blue-purple bits, a little almost-green haze. These were annealed with no striking segment, so at 565C all the way.
Things I want to know:
1) When unencased, is this pretty much what I should expect to get?
2) Green. How?
3) Do you think there are other issues here - am I not getting it hot enough to begin with, apart from any oxy limitations? Does it only get the vibrant colours in blown work?
I'll try reducing it before encasing next time.
Should I just file it under brown? It was handy in eye murrini and jellyfish tentacles for the saturation.
I'll be taking some along next time I visit somewhere with oxygen tanks, to see if I get anything different.
I've been getting really nice results from all the amber purples I've tried and almost everything else too - NS multi is the other frustrating colour so far (I got pale washed-out grey-green in beads when it wouldn't do anything either in the flame or the kiln) but I've not tried it again yet.