Why did my resin color turn brown or yellow?
Common Causes of Discoloration
UV light is a major culprit: epoxy resin is sensitive to ultraviolet rays, which can cause it to yellow over time. This is especially noticeable in clear casts exposed to sunlight. Using a UV-resistant resin or adding a UV inhibitor can help.
Heat generated during curing (exothermic reaction) can also cause browning, particularly if the resin is poured too thick or mixed in a large batch. Excessive pigment or certain dyes can also discolor the resin, especially if they are not lightfast.
- UV exposure from sunlight or fluorescent lights
- Excessive heat during curing (thick pours)
- Too much pigment or non-lightfast dyes
- Some resins yellow more than others
Prevention and Solutions
Choose a high-quality resin labeled as non-yellowing or UV-resistant. Work in a cool area and pour in thin layers to reduce heat buildup. If you need to add color, use pigments specifically made for resin and follow the recommended ratios.
For pieces that will be exposed to light, consider applying a UV-blocking topcoat or sealer. If yellowing has already occurred, it's usually permanent—you may need to sand and recoat, or start over. Testing a small sample before committing to a large project is always wise.
- Use non-yellowing resin
- Pour in thin layers to manage heat
- Use resin-specific pigments
- Apply UV-blocking topcoat
Common mistakes
- Assuming all epoxy resins are UV-stable—many are not and will yellow over time.
- Pouring too thick, which traps heat and can scorch the resin, causing browning.
- Using craft acrylic paints or alcohol inks not designed for resin, which may fade or discolor.
