That definitely sounds like the putty is old. Here is a description:
old green stuff.
Three years outside will do that to a putty.
Here is some info I posted on another forum about the aging of the material:
"As to why the putty ages, here's some background I learned from some mails with polymerics.
The putty cures only as a result of the resin (in the yellow part) and hardener (in the blue part) reacting with eachother. Unwanted curing will happen where the two components meet in the ribbon. But also on the surface of the yellow putty, including that which is covered by plastic. Hardener will excape in the air and can in that way get in contact with the resin. Especially in confined spaces like containers since that will concentrate the amount of hardener in the air. So that's how you get skins. Another thing tha happens during aging is that a liquid component in the putty will "evaporate" (not sure about the exact mechanism, sorry) which will make the mixed putty stiffer.
Aging can occur in weeks (desserts) to months (right here in the Netherlands) depending on temperature. It's been pretty hot over where Polymerics was, so that will explain the skin Sandy mentioned.
Freezing will slow down the reaction. I have some putty there from 2002 which is still in great shape apart from a very thin skin on the edge. This was probably already there when I got it. Keeping the components sealed separatly should also do the trick. I've done this with some ribbon I have here and while it was warm here I've not had problems with skin forming."
As to the names, Duro used to be an original name when it was sold as a repairs putty by Loctite. At a certain moment they decided to drop their supplier and go for a different one. This lead to scuptor hoarding putty untill Sandra Garrity found out it was produced by Polymerics in the US. They were quite surprised since they didn't know of it's use for sculpting. They then worked together to perfect the putty for miniature sculpting and it has been made by them since then. The official name is kneadatite blue/yellow sculpting epoxy putty but in Europe the boxes distributed by Sylmasta carry the text "Duro, the original green stuff" (or something like that). So here it's still often called Duro. Green stuff is just a friendly nickname.
To complete the history, Tom Meier is the sculptor who discovered the use of Green stuff after a little misunderstanding. He had been told epoxy putty was used for miniatures and not knowing which one he picked up green stuff. After some practise it turned out he managed to make much better miniatures than many others with Milliput like putties and many 28mm sculptors switched to GS.
@Alan. When have you had problem with green stuff getting compressed during vulcanised mouldmaking? I've never had that problem. By the way, one reason GS is popular is because it survives this process well. It gives more than for instance Milliput does reducing the risk of broken parts.
Brown stuff is similar to green stuff but is better at taking sharp details and becomes hard after curing making it suitable for sanding and filing. Because of that it's often used for weapons and other edged and mechanical thing. It's also more expensive. I tend to use brown stuff with a little green mixed in to make it stick better.
Janne, I'd replace the GS you have. You can keep the old stuff around to use as filler. You can also mix it in with Milliput to strengthen that or to use like brown stuff is used.
Bye, ming-Hua
