A dip mould is an open-topped cup into which a parison is lowered and inflated, giving a shaped body with a free-formed top. A split mould is two or more hinged parts that close around the parison and give the complete shape with a visible seam. A pattern mould has ribs, diamonds or other designs cut into its interior surface that are pressed into the glass as it is blown.
Part of Glass Blowing and Forming
The three kinds of blowing mould and what shapes each can produce.
The Type Of Mould Decides What Shapes It Can Release
A mould must open or let the piece out. A dip mould lets the piece lift straight out because the top is open and the sides do not undercut. A split mould opens in halves so a shape with a neck narrower than the body can be released. The carrier and the corpus’s Glassblowing article describe them.
| Type | Construction | Gives | Cost |
|---|---|---|---|
| Dip | One piece, open top | Cylindrical or slightly tapered body | Simple to make and use |
| Split | Two or more hinged pieces | Complete shape including top, seam visible | More complex |
| Pattern | Interior carved with ribs or diamonds | Impressed surface pattern | Added carving work |
The dip mould’s free top means the neck and lip still depend on hand finishing.
What You Need
- For a dip mould: a block of wood, iron or fired clay with an open cavity; see Mold Construction.
- For a split mould: hinges or pins, handles, and the cavity cut across a joint line.
- For a pattern mould: carving tools for the cavity surface.
Method: Choosing
Step 1: Does the piece need a narrow neck? If so, a split mould is the only one that releases it.
Step 2: Does it need a finished top? A split mould makes it; a dip mould leaves it to hand finishing.
Step 3: Does the surface need a pattern? Cut it into the cavity of whichever mould you chose.
Step 4: How many pieces? A simple dip mould is enough for a few; a split mould pays off in a production run, as in Bottle and Jar Production.
Common Mistakes
- A split mould with the joint through a patterned surface. The seam breaks the pattern.
- A dip mould for a bottle neck. The neck cannot lift out of an undercut cavity.
- Treating the seam as a defect. The corpus notes a split mould leaves a visible seam; it is a trait of the process.
Safety
Hot glass does not look hot
A released piece and an opened mould lose their glow below about 600 °C and burn skin on contact.
Pinched fingers
A split mould closes hard around a hot parison. Keep fingers clear of the joint and hinge.
What’s Next
- Learn next: Mold Construction — materials and making
- Combine with: Bottle and Jar Production — a split mould in use