There's a wide variety of opinion about polymer clay, ovens, and baking. Also the consensus of the polymer community has changed over the years, so some of the things that might have appeared in books or videos, etc., when polymer clay was more in its infancy are no longer considered true, or as true. What I feel is that everyone should check out the latest info that's out there, and then decide what they feel is right for their attitudes, personalities, etc.
(There are actually several "safety" issues that have been discussed about polymer clay, but most clayers don't have a problem with them because of a few things they door don't do.)
The first thing is fumes
that happen when clays are baked... these are normal smells for baking clay and not dangerous, but those who just don't want to smell them will put their ovens in another room, garage, a bigger room, or use some ventilation... or they simply don't stay in the room with the oven for the whole time of baking. (Btw, some clay brands smell stronger than others, and liquid clay generally smells stronger than solid clay.)
If polymer clay burns
, however, it is "dangerous" to breathe a lot
of it ... but it won't kill you or anything, just add to the total load of bad stuff you've breathed or gotten in your lungs over a lifetime.
Normal baking temperatures for polymer clay are 265-275, and up to 325 for Kato in some circumstances. The burning temp of polymer clay though is 385
or more, so if you're using an oven thermometer and being careful to make sure the temp on the dial is set right, that should never happen.
If it should though, you'll smell a horrible and irritating smell and see thick black smoke billowing out of your oven as your clay turns to a blackened crisp. You probably wouldn't be able to stay in the room even if you wanted to. Just hold your breath, turn off the stove, leave the room and air it out. The danger would be only to something like a small child in a play pen or an animal that couldn't leave who stayed to breathe in a lot
of the smoke.
The other main issues is plasticizers
from the raw clay which can settle on the walls of an oven when the clay is baked. No one knows whether this is actually even a problem, but to err on the side of safety, it's recommended that those who do a LOT of clay baking not bake all
their production work in a home oven (or that they use an "enclosed" baking method for at least part of it(--more on that below).
If they do bake a lot
of clay in that oven, most clayers will clean the oven periodically --I don't know anyone who cleans it every time though, or even close (...keep in mind that oven cleaner is probably more toxic than plasticizer).
Generally though, clayers who decide they do want to get into this will buy a small toaster oven (or convection oven if they can afford it), and use that as a clay-only oven... they may still bake in their larger home ovens if they have taller items, etc.
If one must bake a lot
in a regular oven, or if one just prefers, polymer clay items can be baked inside an enclosure inside the oven (something like two disposable aluminum pans clipped together, etc.), or even have a damp paper towel draped over the item as a sort of enclosure. These methods also have the advantage of moderating the heat in a smaller oven and helping prevent darkening of any projecting areas of the clay (bake time should be increased when using totally-enclosed methods.
There are also issues with a few people being sensitive to the plasticizer in raw clay and liquid clay, and those people may get a rash
after working with them.
Also, it's not recommended to use clay (even baked clay) near food or utensils where it may be ingested
... it is
certified non-toxic by the official craft industry (and there are many dogs who love the stuff and continually produce technicolor poop with nary a problem), but on this one we just try to be ultra-ultra-safe.
Pasta machines and other things with crevices
(or with surfaces which could be a bit porous
) could hold onto some of that plasticizer and release it later into food too, so it's also recommended not to re-use tools like that with food (though many clayers feel that ultra-smooth items without crevices can be well cleaned, and don't worry about those).
Now if polymer clay is baked (properly and thoroughly), all the plasticizer in it will harden with the other materials inside and become "inert" like many other plastics. It's possible
though that some bit of clay may not have been thoroughly cured, and therefore some of it's plasticizer could "leach" out over time onto food utensils or other things it's used on (it could also leave an oily ring on any porous surface). So atain, just to be on the Uber-Safe side, it's recommended that even baked clay not be used in direct contact with the mouth (e.g., a glass wine goblet may be covered with clay, but not on its rim where lips may be).
If you're interested, there's much more about about all of the things I mentioned above, plus much more on the topic of baking polymer
clay, on this page:http://glassattic.com/polymer/baking.htm
And if you want to read more about safety
and polymer clay, check out this page:http://www.glassattic.com/polymer/safety_health_cleaning.htm
Hope that clears up some of the confusion!
--- polymer clay "encyclopedia"http://www.glassattic.com/polymer/contents.htm