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MFG Processes

Press Molding Ceramics

Press molding ceramics forms clay between a die and a rotating profile tool or matched mold, producing flatware and repeat shapes quickly.

Part
Forming
Variants
2
Revised
2026-08-11

At a glance

Family
Glass and Ceramics
Typical tolerances
Roughly ±0.5–1% of dimension for dry-pressed parts and ±1–2% for plastic-formed jiggered and ram-pressed ware. Ceramic tile dimensional classes are defined in ISO 13006 and ANSI A137.1.
Typical volumes
1,000–10,000,000+ pieces per year depending on variant
Lead time
6–16 weeks for steel dry-pressing tooling; 2–6 weeks for ram press dies or jigger molds. Production cycles run about one second (dry pressing) to a minute (ram pressing).
Materials
Ceramic

What it is

Press molding covers the ceramic forming processes that shape a body between tools under pressure rather than by casting or hand work. Three variants account for most production. Jiggering and jolleying press plastic clay against a rotating plaster mold with a profile tool, producing flatware and simple hollow ware in seconds per piece. Ram pressing squeezes plastic clay between two porous dies with an air-release cycle of roughly 20–60 seconds, making non-round shapes such as handles, platters, and cookware. Dry pressing compacts granulated powder at 4–8% moisture in a steel die at high pressure — the process behind essentially all ceramic tile and most technical ceramic blanks.

The reason to press rather than cast is cycle time. A slip casting takes hours; a jiggered plate takes seconds and a dry-pressed tile about a second. The trade is shape freedom: pressing needs an open die geometry, so undercuts and enclosed hollows are out.

Fired shrinkage runs roughly 6–10% for dry-pressed bodies and higher for plastic-formed ware, since plastic bodies carry far more water.

How it works

Jiggering and jolleying

  1. A measured bat of plastic clay is dropped onto a rotating plaster mold that forms one face of the piece.
  2. A metal profile tool — or, on a roller-head machine, a heated rotating roller — descends and spreads the clay against the mold, forming the second face. Jiggering forms the outside of flatware against a convex mold; jolleying forms the inside of hollow ware against a concave one.
  3. The piece stays on the mold while the plaster draws water out, releases at leather-hard, and goes on to drying, bisque, glaze, and glost firing.

Ram pressing

  1. A slug of de-aired plastic clay is placed on the lower die.
  2. The dies close under hydraulic pressure. Both dies are porous, and vacuum drawn through them pulls water from the clay while the pressure forms the shape.
  3. Compressed air is blown back through the porous die to release the part — the reason the dies must be permeable.
  4. Cycle time is roughly 20–60 seconds, and dies are typically a filled resin or specialized plaster with embedded tubing.

Dry pressing

  1. Spray-dried granulate at 4–8% moisture is fed by volume into a hardened steel die.
  2. A uniaxial press compacts it, with tile presses commonly working in the region of 3,600–6,500 psi (25–45 MPa) and cycles around one second.
  3. The green compact is strong enough to handle immediately and goes straight to drying and a single firing in a roller-hearth kiln.
  4. For technical ceramics, isostatic pressing applies pressure hydraulically from all directions at far higher levels — 15,000–45,000 psi (100–300 MPa) — producing uniform green density in shapes such as spark plug insulators.

Design guidelines

Open die geometry only

Every pressing variant needs the part to release from a two-piece tool along one axis. No undercuts, no enclosed hollows, no re-entrant features. If the shape has them, it belongs in slip casting or ceramic injection molding.

Uniform section

Density in a dry-pressed compact varies with the local compaction ratio. A section that is deeper in the pressing direction compacts differently from a shallow one, and the two then shrink differently in the kiln. Keep pressing depth as uniform as the design allows.

Draft

1–3° minimum on dry-pressed parts, more on tall features. Ceramic granulate is abrasive and low-draft walls both stick and wear the die.

Radii and edges

Fillet all internal corners at 0.02 in (0.5 mm) or more, and break external edges. Green compacts chip readily at sharp edges during handling, and fired ceramic chips even more readily.

Aspect ratio in dry pressing

Uniaxial pressing produces a density gradient through the thickness because die-wall friction absorbs part of the applied load. Keep the pressed height modest relative to the width; tall parts need isostatic pressing to achieve uniform green density.

Shrinkage allowance

Dry-pressed bodies shrink roughly 6–10% linearly on firing because they contain little water; plastic-formed jiggered and ram-pressed ware shrinks more. Tooling is sized to the measured figure for the specific body.

FeatureRecommendedLimitWhy
GeometryOpen, single draw directionNo undercutsPart must release from the die
Draft (dry pressing)2–3°1°Abrasive granulate galls the die
Internal radius0.04 in (1 mm)0.02 in (0.5 mm)Green compacts chip at corners
Pressed height:widthLowIsostatic pressing aboveDie-wall friction causes density gradient
Firing shrinkage6–10% dry pressedBody-specificTooling sized to measured shrinkage

Cost drivers

Pressing is a tooling-and-throughput business. Dry pressing has the highest tooling cost — hardened steel dies that must resist an abrasive granulate — and by far the lowest cycle cost, at roughly a second per pressing on a multi-cavity tile press. Ram press dies are cheaper but wear faster and are replaced as consumables. Jigger molds are plaster and cheapest of all, but wear in tens to low hundreds of cycles and must be held in large numbers.

Firing dominates running cost in every variant. Tile is fired once in a continuous roller-hearth kiln; tableware is fired twice. Kiln throughput, not press throughput, is usually what caps a plant's output.

Volume breakpoints: jiggering suits a few thousand to millions of pieces of flatware a year. Ram pressing suits hundreds to tens of thousands of non-round pieces. Dry pressing needs high volume to justify steel tooling and is the standard route above roughly 100,000 units.

  1. Design for a single draw direction; that decision determines whether pressing is available at all.
  2. Keep pressing depth uniform to keep green density and therefore fired shrinkage uniform.
  3. Match the variant to volume — plaster jigger molds for tableware runs, steel dies only at high volume.
  4. Break every edge; chipping in handling is a major scrap source.
  5. Design ware to stack densely in the kiln, since kiln capacity is usually the bottleneck.

Variants

2 named

Jiggering

Ram Pressing

Questions

6 questions
What is the difference between jiggering and jolleying?

Both press plastic clay between a rotating plaster mold and a profile tool. Jiggering forms flatware, with the mold defining the top face of the plate and the tool shaping the underside and foot. Jolleying forms hollow ware, with the mold defining the outside and the tool forming the inside.

What pressure does ceramic tile pressing use?

Tile presses typically work in the region of 3,600–6,500 psi (25–45 MPa) on spray-dried granulate at 4–8% moisture, with cycles of roughly a second. Technical ceramics needing uniform green density through a tall section use isostatic pressing at 15,000–45,000 psi (100–300 MPa) instead.

Why must ram press dies be porous?

Vacuum is drawn through the dies to pull water out of the plastic clay while it is being formed, and compressed air is then blown back through the same porosity to release the part. Without permeable dies, neither the dewatering nor the release would work.

Can press molding produce undercuts?

No. Every pressing variant needs the part to release from a two-piece tool along a single axis. Undercuts, enclosed hollows, and re-entrant features require slip casting or ceramic injection molding instead.

How much does a dry-pressed ceramic shrink?

Roughly 6–10% linearly on firing, considerably less than plastic-formed or slip-cast ware because the granulate contains only 4–8% moisture rather than 20% or more. Tooling is sized to the measured shrinkage of the specific body.

Why does dry pressing produce a density gradient?

In uniaxial pressing, friction against the die wall absorbs part of the applied load, so regions further from the punch see less pressure and compact less. The result is a green density gradient that becomes a shrinkage gradient in the kiln. Keeping pressed height low relative to width limits it; isostatic pressing eliminates it.