I haven't used Oommoo, but I'd recommend letting it warm upstairs.  If that doesn't do the trick, then see how deep the hardness goes.  Try to poke through it, as maybe only some of the stuff at the top has hardened.  If that works, then toss out the hardened part and strain the rest into a new container.

I had a similar thing happen with Polytek Easyflo 60.  Both part A and B were in the same "ketchup squirter" type containers, but part A got cloudy and hardened a bit.  I just strained it with some pantyhose I borrowed from myself, into a new container.  Either something contaminated it, or it had some sort of photosensitive reaction...

It's a Phenomenon!

I based the extra armor off the ARC Trooper from the Clone Wars series.  If you look at the pics from the link below, you'll notice the chest armor is different from right to left.

ARC Trooper photos at RS

Thanks Brisk.

Unfortunately, I was never very good with Sculpy.  I'd sculpt a piece, boil it, and try to sculpt more on the same part, but Sculpy was too brittle and would either flake or break off. 

If I had any advice for Sculpy, I'd say:

1.  Invest in some good sculpting and/or dental tools
2.  Don't overboil the part, or it becomes way too brittle.  30 seconds is usually more than sufficient if the part is not too thick.
3.  Be patient with yourself.  It's sometimes discouraging when a slip of the hand or tool ruins a part you've worked on forever.  Just know that you WILL screw up at some point.  Roll with the punches that sculpting small stuff throws at you, and try, try again.  You won't create your masterpiece the first or even 50th time you sculpt something.
4.  Use a separate pot for boiling Sculpy. 
5.  If you try Sculpy for a month and don't find it to your liking, order some Fixit Sculpt from AvesStudio.com.

Not quite finished with my 4 ARCs, but here are some teaser pics:

I hope my painting has improved over this:



Talk about superchunky...

No probs Noodle.

The "syringe" was bought at a Hobby Lobby for 10 bucks.  It's a Sculpey product, so I'm sure you could find it elsewhere.  Here's a pic of what it looks like:

.

It comes with attachments that'll make circular, triangular, square, rectangular, and even 3-leaf clover beads!  Yay!  It will certainly make thinner strands.  The only drawback to using it with Fixit is it's difficult to clean.  Make sure you dip the syringe in water before you put the Fixit in.