From Clay to Porcelain: How Many Steps a Bowl Takes

Overview: nine steps down the line

The mainstream route in a modern dailyware plant is mechanised forming plus roller-kiln firing. The nine steps below are the shared skeleton for almost all bowls, plates and cups; bone china, strengthened porcelain and colour-glaze ware differ mainly in recipe and firing schedule, not in step order. Once you can see this chain, quotations make sense: “irregular form”, “in-glaze decoration” and “high whiteness” all cost more because each adds a step or lowers yield.

1. 01

   Raw materials & batching

   Kaolin, feldspar and quartz are weighed to recipe, wet ball-milled into slurry, screened, de-ironed and aged.

   Sets whiteness & plasticity
2. 02

   Forming

   Slip casting, roller pressing, dry pressing or throwing turns the body into a wet blank.

   Sets wall-thickness evenness
3. 03

   Drying

   Air or hot-air drying brings moisture down to a handleable level.

   Controls warping & cracking
4. 04

   Fettling

   Burrs, rims and foot rings are trimmed and sponged for dimensional accuracy.

   Sets rim feel
5. 05

   Bisque firing

   A first firing around 800–900°C gives strength while keeping the porosity needed for glazing.

   Bone china differs — see below
6. 06

   Glazing

   Dipping, spraying or brushing; the layer must be even, with no runs or bare spots.

   Sets gloss & touch
7. 07

   Glaze firing

   High-temperature firing at roughly 1200–1400°C vitrifies body and glaze under tightly controlled atmosphere and ramp curves.

   Sets strength & porosity
8. 08

   Decoration & decal firing

   Decal, print or hand painting, then a low-temperature decorating kiln; in-glaze work returns to high heat so the design sinks into the glaze.

   Under / in / on glaze
9. 09

   Inspection, grading & packing

   Every piece is checked against national standards for appearance, dimensions, deformation and glaze, graded, then packed.

   Drives arrival defect rate

Recipe: whiteness and translucency are formulated, not polished in

The classic dailyware triad is kaolin (plasticity and structure), feldspar (flux, lowering firing temperature) and quartz (structure, resisting deformation) — typically near 50/30/20, tuned to local materials. Impurity control is the first gate on whiteness: iron and titanium oxides leave dark specks and colour shift, so slurry is magnetically de-ironed and screened. Premium lines add repeated filtration; the “seven filtrations, five screenings” process published by a leading Huairen producer is an intensified version of this stage, reported to lift whiteness and translucency indicators by more than 10%. Glaze must be matched to body: mismatched thermal expansion produces crazing on cooling.

Forming: four methods, four cost structures

Forming method drives unit price, throughput and how complex a shape can be. Round ware (bowls, plates) is cheapest by roller pressing; handled cups and irregular vases must be slip cast; dry pressing suits regular flat pieces; hand throwing appears only in art ware and small bespoke runs. This is why “irregular-form ware” is counted as its own product series in Huairen: high-pressure slip casting needs more complex moulds and a longer forming cycle.

Firing: temperature decides which porcelain it is

Firing is the least reversible step. Conventional dailyware runs low-temperature bisque then high-temperature glaze firing: 800–900°C first for strength with retained porosity, then 1200–1400°C to vitrify. Bone china inverts this, using high-temperature bisque and low-temperature glaze firing: bisque at 1240–1255°C matures the body first (the trade calls it “biscuit” or “bone”), after which it is sorted, polished, hot-sprayed with glaze and fired again at 1100–1150°C. The reversal exists to handle bone china's narrow firing window, high shrinkage and tendency to slump at high heat, while still yielding a bright glaze. Setting uses thin-walled profiled saggars with inverted and rim-supported stacking to hold the form true. Strengthened porcelain instead adds alumina and magnesia and fires around 1340°C for higher impact strength. Cooling matters just as much: quartz inverts near 573°C, and cooling too fast through that band cracks ware outright, so the slow-cool zone needs a deliberately designed gradient.

Decoration: under-, in- and on-glaze is a safety question too

Where the decoration sits relative to the glaze determines abrasion resistance, whether it touches food, and how much heavy-metal migration risk it carries. Under-glaze work is painted first and sealed entirely beneath the glaze. In-glaze work is fired into the glaze layer, balancing expressiveness with durability. On-glaze work is fixed on top at low temperature — brightest and cheapest, but exposed to wear, and bright yellows and reds have historically used cadmium sulfoselenide pigments. That is precisely why regulators single out the 2 cm lip zone for lead and cadmium testing. Specifying the decoration method, not just “printed”, is what actually controls this risk.

Inspection: what national standards let you verify item by item

Dailyware quality is not judged by feel — national standards define a full test system that a purchase contract can cite directly. Defect types follow GB/T 3303; dimensional error and defect size follow GB/T 3301; deformation GB/T 3300; water absorption GB/T 3299 (bone china must not exceed 0.5%); thermal shock GB/T 3298 (small bone china pieces must survive a 140°C to 20°C differential); microwave resistance GB/T 27587; mechanical-wash resistance GB/T 32680; and fridge-to-microwave-to-oven suitability GB/T 34253. Pieces are graded first, second or qualified by weighted defect count. Citing these numbers in an order gives both sides a shared language at inspection.

GB/T 13522-2024 Bone China (drafting bodies include Huairen Jintai Ceramics) ↗

Huairen's process position: coal-basin kilns and automated lines

Huairen sits in the Datong coal basin, and abundant coal historically meant hot, comparatively stable kiln control — the explanation usually given for why local black-glaze oil-spot speckles look full, even in size and orderly in spacing. The modern district has moved that kiln knowledge onto an industrial platform: 80 automated line sets among 123 production lines, a leading share nationally. Raw materials, forming, decal firing, packaging, ceramic machinery, kiln furniture, kiln construction, mould making and transfer-paper design are all chained locally, so changing a pattern or a mould does not require cross-province coordination. Local firms have co-drafted the GB/T 13522-2024 bone china standard, where Huairen Jintai Ceramics appears in the list of drafting organisations.