Polymer clay does not have a "shelf-life". It can be stored for years, become hard as rock and, if it was stored at temperatures not over 90F (at which point some of it might get half-baked) you can re-condition and use it as if it were brand new.
Depending on what part of the world you are in, you will have access more easily to various brands of polymer clay. Let's discuss them a little bit.
Sculpey makes three major lines and a few more varieties that are usable in making polymer clay jewelry, decorative objects and sculpted figurines.
My advice is – stay away from it. Sculpey III is a polymer clay good for kids to play with. It is the most brittle of all polymer clays, no matter how long and how hard you bake it. After it's baked, it will degrade in time and months after finishing your pieces you will find beads cracking all of a sudden or your painstakingly sculpted figurines starting to lose their fingers, noses and ears.
Use only if you're out of everything else, or sparingly in mixes for specific colors. The only one that I personally use is the glow in the dark, mixed with Premo, only for Halloween fun jewelry projects. I had my bad experiences with it in the past so I'm staying away from it.
One of the most widely used polymer clays in North America. The most readily available. Very hard after baking (if baked properly) . Can be used in very thin pieces too and the pieces will be bendable and very resilient. Might have the tendency to become too soft and might require “leeching”. Good for making canes too, but due to the tendency to become soft you might have to let your canes rest for a while while reducing them and definitely before cutting them.
Comes in a large variety of colors. The “Accents” line of Premo has also various colors of polymer clay with glitter inclusions and with mica powders – depending on the colors, the mica powders ones are either “pearlescents” or “metallics”. Can make very realistic looking faux metal and faux gemstone. The translucent of the Accents line comes in three varieties: normal, white and opal. The normal has an offwhite hue, good translucency, but in humid environment has tendency to plaquing. If baked too long might get a yellowish tint. The “white translucent” is slightly whiter than the regular but not by much. The “opal” is just the white translucent with iridescent glitter inclusions.
Souffle is the newest line of Sculpey and is practically the re-formulated Studio line with a bit more stiffness and less phtalates. It has a wonderful feeling to the touch, and usually it's almost ready to use out of the package. When working with it it feels like suede to the touch. It seems a little soft but it is very firm in fact, does not “smudge” easily and keeps minute details very well. The best polymer clay for canes. It might present an interesting powdered look when used in skinner blends (gradients). Comes in a variety of “softened up” more earthy hues the same as the old Studio line.
Not very different from Sculpey III, it comes in bigger packages and in the natural clay colors, white, greyish and terracotta. Good for making prototypes or let kids explore their creativity
An excellent clay for doll sculpting. It does capture that translucency that natural skin and flesh have. The only drawbacks are the color – in only comes in a beige that darkens a lot when baked, so all your dolls will have a super-tan look, and due to the amount of translucent clay it contains it will have the tendency to plaquing. It can be mixed with other clays though to change the color. Very resilient after baking if baked correctly, and can be used for minute details like delicate doll fingers and elf ears.
I would call it the best for decorative objects especially when trying to imitate stone or metal. Feels a little harder to condition but keeps the detail exceptionally well. Good hardening and resilience after baking. Only comes in a darker grey color.
An excellent clay for sculpting dolls. I would suggest to mix some Super Sculpey or just a bit of translucent in it for a more realistic effect (depends for what color skin you are going for). Keeps detail very nicely. Comes in three different skin hues, light, beige and baby.
It's actually a mix of Super Sculpey and Super Sculpey Firm. Less hard than the Firm but a little harder than Super Sculpey by itself. Comes in a lighter grey than the Firm. Honestly it would make more sense if they'd have a mix of Super Sculpey and Living Doll - that would give the Living Doll the translucency it lacks and make Super-Sculey's color more natural and changing less once baked.
If you approach this clay without the expectation of making finished beads and focals just with it, you will not be disappointed. Ultra-light was not created to be used by itself in jewelry. It is mostly used as a filler/armature for bigger pieces. So if you want to make a huge focal. The best it is to use Ultra-light for the inside part and then cover it up with any other polymer clay of your choice. If you try to use this clay by itself, you will find it too soft (doesn't really leech to workability) and impossible to hold detail.
It's just a Sculpey III that has phosphorescence and glows in the dark. The rest is exactly as Sculpey III, so I wouldn't recommend it by itself for any projects that you'd like to last for a while.
As much as it was initially designed for children, you want to have this always handy. It's one of the best and cheapest choices for making your own texture sheets, because it can hold very decent detail but also after baking, as the name says, it is flexible, so the texture sheet will be almost like a rubber texture sheet.
Sculpey Model Air clay
This line doesn't need baking, but you have only a certain amount of time to work it as it's self-hardening. You can make decent beads with it and it sands and buffs well. It used to come in two colors only, but now to the Terracotta and White has been also added Porcelain..
A specialty clay that is generally used to make molds. It is excellent also for various repairs, not just for polymer clay issues, but also for cracks and other damage (as long as the object can be baked). It can also be used to soften very firm polymer clay.
Until not long ago, there was only one in this line, the one known for years as TLS – translucent liquid sculpey. The translucency of it was (and is) not that great but it's the go-to medium to use when ensuring that raw clay bonds with baked clay.
The new comers to this line are the Clear, White, Black, Pearl, Silver and Gold. The colored ones are, well, colored. I found the “Clear” to be more watery than the traditional one, with more translucency but it's still far from Fimo and Kato translucent liquid clays. It does hold bond as good as the traditional one.
Other special items from Sculpey:
Designed to work for softening Polyform polymer clays, I can assure you that it works just fine with Fimo and Cernit also. Just don't use it with Pardo, and especially not with Pardo of the Translucent line, it will seriously affect the translucency - Pardo has a completely different plasticizer formula that is not very compatible with the softeners for other clays.
Do not confuse it with Sculpey Bake and Bend. This is a liquid and it is used to ensure perfect adherence between baked and raw polymer clay. It is true that you can use liquid polymer clay for that, but in my experience the Bake and Bond is way stronger. Also, it's almost half the price of the liquid clay of any brand, so....
They come in Gloss and Satin. I personally am not very fond of them as there are way better alternatives out there, but if that is what you have handy, go ahead and use it. Just be careful, you will need a very good paintbrush, as it has the tendency to streak and get air bubbles. Also, as with any other Satin or Matte varnishes make sure that if you use the Satin, you first stir it really well, as in these type of varnishes the "matte-ing" elements have the tendency to settle at the bottom, and if you don't stir, even with the Satin you will get a glossy finish.
Fimo by Staedtler
Fimo is the second most available brand in North America. It comes in several lines of which the most known are Classic, Soft, Effects and Professional. There are also special clays for dolls and figurine sculpting. Fimo is a quite hard clay and most artists find it much harder to condition than other clays. If you have any issues with your hands, like arthritis, or if you don't have a pasta machine, avoid buying Fimo. Fimo has gone through reformulation in 2007 and the baking temperature was reduced from 265F to 230F. I will only talk about the bakeable here even if they have an air dry one - I never tried it.
The hardest of all the Fimo lines, it will present problems at conditioning. It also doesn't blend easily, but it holds detail very good. Does great in cane work, due to the firmness and ability to hold detail. Comes in 24 colors including translucent. To be noted that the Staedtler (the Fimo manufacturer) website does not list Fimo Classic anymore in its lines of products, but it can still be found on the North American market sometimes. It has been replaced officially by Fimo Professional
The easiest to condition clay of the bunch, has the drawback of not holding detail that well. Also, since reformulation it has lost a lot of durability and is now as brittle as Sculpey III. It comes in 52 colors including some special effects (inclusions and transparency) ones.
This line has all kind of effects – glitter inclusions, mica powders – this is where you will find the metallics and pearlescents. It is relatively easier to condition than Classic but harder than Soft. Detail holding is ok and so is durability and flexibility after baking.
The latest in the Fimo line, Fimo Professional's specialty is color. Of all the polymer clays, here you will find the truest colors - there is actually a "line within the line" that is the True Colors. A little bit easier to condition than Classic but not by much. Also doesn't blend and smooth too well, but buffs to a wonderful shine. Great for cane work and anything detail as it holds detail very well. Good durability and flexibility after baking. Also to be noted is that because of the "pure colors" you won't get surprises if you want to mix a new color like you might with other clays - you can confidently mix colors using the color wheel for good results.
Puppen Fimo/Fimo Professional Doll Art clay
If you want to go more for OOAK dolls and figurines, these is THE clay to go for. Better than Super Sculpey and also comes in a variety of flesh tones. Has a wonderful detail retaining capability, gets smoothed and blended and finished to high quality.To be honest, I used both "brands" and it's actually the same clay, only that it's sold as Puppen Fimo for the European market while Fimo Professional Doll Art clay is the name for the North American market. After all, “puppen” in German means “doll”. It comes in 6 beautiful skin tones, but very careful each of them is in an "opaque" and "semi-opaque" variant. I personally prefer the "semi-opaque" as it has the beautiful translucency of real flesh. In the name of the colors, I give you links to the opaque versions as I couldn't find semi-opaque for all the colors. It comes in Porcelain, Beige, Cameo, Sand, Rose and Nougat.
The Fimo name for their transparent liquid clay. One of the best and most transparent liquid clays on the market. The only drawback is that it will not cure to glass-like hardness like Kato does. It will always have a mild softness/stickiness to the surface even when the curing is finished with the heat gun. Special attention must be paid to the tendency to make air bubbles. Even with the drawbacks it is the best to use for making dolls eyes, as it domes more than Kato liquid. It also has a mild scent, not as strong as Kato liquid though, and even if you get a few air bubbles they are really easy to get rid of. I will make soon a tutorial or article on how to avoid air bubbles in transparent liquid clay and I will address this issue
The Fimo variant of what the Clay Softener is for Sculpey. It is not in liquid form though, and is used to soften up hardened Fimo clay. I personally never used it, I used the Sculpey clay softener and it worked fine.
Kato comes in only one line. This is a polymer clay close to the hardness of Fimo classic. Quite hard to condition but holds the detail very very well and, after Souffle, it's one of the best to use in cane work.
Be aware though that it is the “smelliest” of all polymer clays. You might not be able to get used to the specific smell as it emits quite a bit of it when baking. I personally do not use it anymore as my pets seem to go through fits of throwing up every time I bake Kato. It comes in 21 colors, including translucent and metallics. The Kato translucent clay is the least translucent of all and yellows quite a bit when baking.
The best of liquid clays. It cures to a beautiful glass-like appearance, the transparency is 100% and the surface is fairly hard. It's so good that you can actually use it as a varnish, using a heat gun. It will make a mirror-like finish and can be used instead of resin on curved surfaces.
One of the best polymer clays out there (for me personally it is THE best), but not readily available on the North American market. Fairly easily to come by in the European market. The fact that it has beeswax in the composition makes it pleasing to work with, on one hand , but might take a while to get used to the consistency before full conditioning, as it will feel more “waxy” and will have the tendency to crumble if you try to condition it the way you condition all the other clays. It will condition beautifully if you know how to condition it - please see my tutorial on conditioning Pardo clay. To be noted that if conditioned improperly, Pardo (especially in the Transparent line) will plaque and it might also release on the surface a waxy residue after baking. If that happens, my advice is to re-do that piece as the gelation did not happen properly and your piece might be brittle. All Pardo holds detail exceptionally. It comes in four lines.
Art Clay comes in 13 highly pigmented colors. Unlike most other clays (except Fimo Professional) the colors can be mixed for true results without muddinness as they are “true colors”. Art Clay holds exceptionally fine detail and is great not just for cane work but also for filigree work.
Jewelry clay comes in a variety of colors (52), all imitating either gemstone or metal, and the names of the colors themselves are reminiscent of the respective gemstones or metals. Some of these are pearlescent, some are more opaque and some have some translucency. Also in the Jewelry line there are several colors that have glitter inclusions. I am preparing an information chart to show you which has translucency, which has pearlescence and how the color changes at baking - and hopefully soon some color recipes. This, combined with the Transparent line, is THE clay to create faux gemstones and faux metal jewelry.
Pardo Transparent Translucent is the most translucent of all polymer clays. The line of transparents comes in 8 true colors. If you are looking at trying some gemstone imitation techniques that involve transparent gemstones, this is the clay to go to. It is to be noted that Pardo Transparent Translucent Clay presents a lot of problems for the neophites to the world of polymer clay, due to the fact that - being based on bees wax - it can get a lot of plaquing if not properly conditioned and manipulated. Some people like that for making faux gemstones - I personally find that the random plaquing does not improve the realistic look of a faux gemstone, on the contrary - especially because in crystals (for which one uses translucent clays) the fractures do not happen in a round shape (the shape that plaquing has) but have to be re-created in clay following the natural fracture in a crystal - which is a straight line or plane. Due to the beeswax, if not conditioned properly, Pardo will get a lot of plaquing from tiny droplets of moisture (which is the cause of plaquing in Pardo, not air bubbles). There are specific ways to condition the Pardo transparent translucent to obtain good, non-plaquing pieces, but even so, if you are trying to do that on a rainy day, better leave it for when it stops raining, if you can't run the A/C to remove the humidity in the air. Also, very important to note, Pardo Transparent - and especially the Transparent Translucent, is opaque until baked AND cooled. The Translucent Transparent will be white, and if you need to re-bake a piece it will become white again, and regain the transparency once it cools off. I personally found that on this specific clay the "dunk in iced water" is not a myth, but a real fact. Check my tutorials that involve using Transparent clays for gemstone imitation techniques and you shall see how, due to proper conditioning and the "ice water dunk" I get superb, non-plaqued transparency/
The Mica line comes in 5 colors - Platinum, Silver, Gold, Copper, Bronze. The amount of mica powder seems to be higher than the same colors in the Jewelry line and also with some translucent mixed in, makes it the best for the mica shift technique. It is slightly softer than the Jewelry line. The mica particles, both in the Mica line and in the Jewelry line are way finer than the Premo Accents line, but even if that makes the mica shift less flashy, it provides a superb faux metal look without any enhancements, once the clay is sanded and buffed. Also, due to the exceptional detail holding of this clay, you can achieve pieces as spectacular as if you would if you would use PMC (Precious Metal Clay)
Pardo does not have a liquid clay line. It does have a “jewelry laquer” that is just a varnish applied on finished pieces.
Another European (Belgium) polymer clay not very easily available on the North American market.
I honestly had only sparingly worked with Cernit and that was before the reformulation it went through . I do intend to try it sometimes in the future and I will write here on my experience on it.