What causes seedy in the glass? Is it normal?
- kodchaponhk
- May 21
- 2 min read
This is a great question! Seedy, or what we call "the tiny bubbles in the glass", has a clear explanation like this. What is Seedy in Glass? “Seedy” refers to tiny air bubbles or cloudy spots that are scattered in the glass. They are usually seen as tiny spots or marks that look like air bubbles, hidden inside and not on the glass surface.
What causes them? These bubbles occur during the glass melting process, especially in glass produced using the blown glass or hand-crafted glass processes, or in stained glass that still uses traditional techniques, such as stained glass, which will have tiny air bubbles stuck to the mixture that still has gases or impurities left during melting.
Is this normal? In art glass / blown glass / stained glass, air bubbles are common and are often considered a signature of handmade glass. These bubbles give the glass a more “life” or textured appearance than smooth industrial glass. However, in modern architectural glass such as float glass, these bubbles should not occur as they are considered a manufacturing defect.
Summary: In Art Glass: Seedy = Natural + Charming
In General Building Glass: Seedy = Flawed / Failed QC
If you are using Seedy glass in art, such as stained glass panels, it is “charm”.
In addition, there are common “defects” in handmade glass that are considered natural processes.
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.
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