What causes seedy in the glass? Is it normal?
- kodchaponhk
- May 21, 2025
- 2 min read
Updated: Jan 25
This question comes up very often, and it's something many people wonder about. The term "seedy," often used by glassmakers, actually refers to tiny air bubbles embedded within the glass itself. They aren't on the surface but are visible as small, clear or cloudy dots, similar to air bubbles.
These bubbles form during the glass melting process, especially in handcrafted glass like blown glass, handmade glass, or stained glass. Because the manufacturing process doesn't ensure a perfectly smooth surface like industrial glass, small amounts of air or gas are trapped within the glass. When it cools, these bubbles form.
In the world of artistic glass, seedy bubbles aren't considered a drawback. On the contrary, many see them as a charm, a signature of handmade work, giving the glass a lifelike quality, dimension, and texture. When light shines through, it appears more beautiful and deeper than smooth, factory-made glass.
However, for general building glass, such as float glass used for windows, doors, or glass walls, these air bubbles are considered undesirable. They indicate a manufacturing problem and are seen as a defect, failing QC standards.
In short, for artistic glass, blown glass, or stained glass, seedy bubbles are a natural characteristic and a charming feature.
However, in typical architectural glass, seedy bubbles are a manufacturing defect.
If you're using seedy glass in artwork, such as stained glass panels, it's considered a unique charm.
Seedy (small air bubbles) Tiny air bubbles in the glass, often found in traditional blown or stained glass, give an antique, classic, and textured feel.
Waviness (Irregular Mirror Surface) The surface may have slight waves or an uneven feel when reflecting light. This is a result of hand-blowing/ironing, which gives the light passing through a playful effect and the shadows cast are not flat.
Striations (thin lines in the glass) are lines or waves in the glass that are caused by the movement of hot glass during melting. They are natural, soft patterns and are not scratches.
Color variation (uneven color throughout the sheet) Some areas are darker, some are weaker, or have uneven gradations, especially in colored glass such as opalescent, cathedral, or streaky glass, adding depth to the light and atmosphere of the piece.
Bubbles / Air pockets (medium sized bubbles) In fused glass, larger bubbles may form from multiple layers of melting. If positioned correctly, this is a feature, not a defect.
Tool marks, such as pliers' clamp marks or the light tap marks of a wooden stick in a blown glass, indicate the "craftsman's handwriting" and genuine handwork.
Conclusion: Each piece of handmade glass is unique. These flaws are not disadvantages...but traces of the process and spirit of the craftsman.