Polymer clay is a modeling and sculpting material that is popular among artists, crafters, and hobbyists. It can be shaped and molded into a variety of artworks, jewelry, decor items, and more. Polymer clay remains flexible and workable until it is baked or cured in an oven, allowing artists to continuously shape and refine their creations before hardening them into their final forms.
What is polymer clay?
Polymer clay, also known as oven-bake clay, is made from polymers such as polyvinyl chloride (PVC) and plasticizers. It is a type of plastic that can be molded and shaped like clay but requires heat from an oven to permanently harden it. The polymers give it plasticity and ability to harden, while the plasticizers keep it malleable and flexible.
Some of the most popular brands of polymer clay include Sculpey, Fimo, Premo, Cernit, and Kato Polyclay. They come in a wide variety of colors that can be blended and mixed to create custom colors as needed. Polymer clays are oil-based, so they will never dry out, but the oil allows them to remain flexible and workable at room temperature.
How long does polymer clay last before baking?
One of the great advantages of polymer clay is its nearly indefinite shelf life before baking. As long as it is stored properly, polymer clay will never dry out or expire. Most brands claim their clay will keep for many years and can even be passed down through generations of artists.
Polymer clay should be stored in a cool, dry place away from direct sunlight and heat to prevent damage over time. As long as the clay is kept sealed in an airtight package, it will remain soft and pliable indefinitely. It does not require refrigeration and has no expiration date.
Many polymer clay artists report using clay that is 5, 10, 20 years old or more that still works perfectly fine. As the clay ages, it may become stiffer and need some kneading or conditioning to restore softness and pliability. Old clay can also discolor or develop a oily film on the surface, but this does not affect workability.
How to prolong shelf life of polymer clay
To keep polymer clay workable for as long as possible:
- Keep unused clay sealed in plastic packaging or airtight containers
- Store clay blocks and packages away from heat, humidity, and direct light
- Avoid extreme temperatures – do not freeze clay or leave in hot areas like cars
- Knead stiff clay to recondition it and add plasticizer if needed
- Rewrap used clay tightly in plastic wrap or airtight bags
- Clean clay work surfaces to avoid dust, dirt, and oil buildup
With proper storage methods, most brands of polymer clay will retain good workability for at least 10-15 years. Some artists report clay being usable for 20+ years. The plasticizers in the clay prevent it from ever fully drying out.
Does polymer clay expire after baking?
Once polymer clay has been cured or baked in an oven, chemical reactions cause it to harden permanently. At this stage, it has essentially become a plastic and is no longer workable or moldable like clay.
Hardened polymer clay pieces do not have an expiration date or finite shelf life. They should retain their shape and colors indefinitely unless exposed to direct sunlight for prolonged periods or extreme heat.
Baked polymer clay is durable but can gradually break down over decades when subjected to sunlight exposure. To extend the usable lifetime of finished polymer clay objects:
- Avoid displaying in sunny windows or direct light
- Use UV resistant sealers/finishes
- Protect surfaces with acrylic paints or varnishes
- Store in cool, dry places away from heat sources
With reasonable care, most sources estimate baked polymer clay artworks and crafts can easily last for 50-100 years, if not longer. The baking process permanently sets the clay, so it does not undergo additional chemical changes that could cause it to expire.
How long does it take polymer clay to cure?
Curing or baking polymer clay causes an irreversible chemical reaction that hardens it into a solid plastic. Cure times depend on the oven temperature and thickness/size of the pieces:
- Thin items: 15-20 minutes at 275°F
- Thicker items: 25-45 minutes at 275°F
- Extra large/thick pieces: up to 1-2 hours at 275°F
The standard baking temperature for polymer clay is 275°F. Higher temperatures around 300°F will speed up curing times slightly but may increase risk of scorching or discoloration.
Always check package instructions, as curing times can vary between different brands. Pre-heating the oven is usually recommended to ensure it reaches the proper temp. Baking for longer than needed is safe and ensures clay is fully cured.
Let pieces cool fully before handling after baking. Clay continues curing and hardening as it cools down to room temperature after being removed from the oven.
Can you store baked polymer clay pieces together?
Finished and cured polymer clay pieces can be stored together without risk of sticking, melting, or damage. Since baking chemically hardens the clay into plastic, items will not fuse or distort once cured, even when touching.
Polymer clay artists recommend nesting and stacking items for convenient storage. Finished pieces like jewelry, figurines, and decorative items will not stick or deform each other after baking. Having contact between objects is not an issue.
The main considerations for storing cured clay are protecting from dust, dirt, sunlight, and heat over time. Placing pieces in airtight containers or covering with fabric is recommended for long term storage and display.
Can you re-bake polymer clay?
It is possible to re-bake cured polymer clay pieces if needed for repairs, attaching new clay parts, or smoothing joints/marks. While clay cannot be reconditioned or reused once baked, additional baking will not damage or destroy properly cured items.
Reasons to re-bake polymer clay:
- Add fresh clay for repairs, extensions, or new detailing
- Smooth seams, fingerprints, or imperfections
- Attach baked pieces together with fresh clay
- Improve strength of delicate areas
Tips for re-baking polymer clay:
- Only re-bake once or twice for best results
- Bake at slightly lower temp (260°F) to avoid scorching
- Support items if needed to prevent warping
- Watch closely to avoid over baking
While polymer clay can technically be re-baked multiple times, the plastic will gradually break down with repeated heating. Limit re-baking to 1-2 additional times for best results.
Does polymer clay melt in the oven?
Polymer clay will not melt, distort, or lose its shape when baked at the proper temperature. As it heats up, the polymers cross-link together forming permanent plastic that will retain its molded shape.
Baking at too high of temperature can risk scorching or discoloration, but will not cause properly cured pieces to melt or slump in the oven. Brands are formulated not to melt at baking temps.
Polymer clay baking problems related to melting/distortion typically occur when:
- Oven temperature is too high
- Item is too thin or has delicate areas
- Piece contains an internal armature or unstable core
- Clay is under-conditioned or under-baked
Maintaining oven temps around 275°F ensures polymer clay will harden smoothly without melting or deforming. Larger, heavier items may require additional internal support to hold shape while curing.
Can you microwave polymer clay?
Polymer clay should never be microwaved. It contains PVC plasticizers that can release hazardous fumes or possibly ignite when microwaved. Microwaving may also create hot spots that scorch the clay.
However, low power microwaves can be very effective for drying solid clay items after baking. This speeds drying time after removal from the oven.
Tips for microwave drying baked polymer clay:
- Only use for dried clay – never soft, uncured clay
- Keep power below 50% to prevent heat damage
- Go for short bursts like 1-2 minutes max
- Allow to cool fully between cycles
- Watch closely to avoid overheating
Again, microwaving should only be done on cured clay items to remove moisture. Never attempt to bake, harden, or condition polymer clay in the microwave oven due to safety concerns.
Can polymer clay be reconditioned after baking?
Once polymer clay has been cured by baking, it can no longer be softened, conditioned, or reworked. The heat permanently hardens the plastic so it will keep its solid shape at room temperature.
Attempting to knead, roll, or reshape baked polymer clay will not work. At best, it may break apart or crack where over manipulated. The chemical properties change once heat is applied, preventing reconditioning.
If polymer clay becomes too stiff, brittle, or dry before baking, it can be reconditioned to restore plasticity and workability. But this must be done prior to curing. Clay cannot be reused or repurposed after baking.
Can you rebake old polymer clay?
Previously baked polymer clay pieces can be safely rebaked as needed for repairs or alterations. While the clay cannot be reconditioned or restored to a flexible state, additional baking will not damage or degrade properly cured clay.
Reasons to rebake old polymer clay:
- Smooth blemishes or fingerprints
- Fill small cracks or gaps
- Attach new clay parts or decorations
- Improve strength of fragile areas
However, there are some best practices for rebaking old clay:
- Rebake at slightly lower temperature (260°F)
- Support or strengthen delicate areas first
- Limit to 1-2 additional bakes
- Watch closely to avoid scorching
While polymer clay can technically be rebaked multiple times, the plastic will gradually lose strength and durability. Keep additional baking to a minimum for items that need touch ups or repairs.
Can you put liquid polymer clay on baked pieces?
Liquid polymer clays provide an easy way to bond clay pieces, fill gaps, create glazes, and more. Since they remain flexible after curing, liquid clays can be applied to already baked pieces.
Advantages of using liquid polymer clay on baked objects:
- Works as a strong adhesive for clay parts
- Allows adding details without rebaking the entire piece
- Fill cracks, gaps, or seams in cured clay
- Create custom finishes and glazes
Most liquid clays brush or trowel smoothly onto baked polymer clay. Allow any additions to cure fully in the oven before use. Finished items can then be sanded, buffed, and polished as needed.
Conclusion
With proper storage and care, both raw and cured polymer clay can remain in usable condition for many years. Unbaked clay stays malleable indefinitely when sealed in airtight packaging. Finished pieces will not degrade for decades if protected from heat and sunlight.
Polymer clay never truly expires, but may become stiffer and require conditioning as it ages. Old or previously baked clay can be restored with kneading or revitalized in the oven. With reasonable lifespans of 50-100+ years, projects and art made from polymer clay can even become family keepsakes or heirlooms.
