Chapter IV · The Vessels · Section 2: In Tang context — reading “鍑以生铁为之其内模土而外模沙土滑于内易其摩涤”

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Thesis

“鍑以生铁为之其内模土而外模沙土滑于内易其摩涤” only becomes legible inside Tang tribute tea, monastery tea and literati life.

Text

“The fu cauldron is made of raw iron. Its inner mold is clay, so the inside is smooth and easy to scour; its outer mold is sand, so the outside is rough and endures the flame.”

Context

鍑（fù）：煮水的锅。内壁用土模使其光滑易洗，外壁用沙模使其粗糙耐烧。

Evidence

• Collation: “其内模土，而外模沙”：百川学海本作此，四库本同；历代注家对"模土模沙"的铸造工艺阐释一致。
• Existing readings: 吴觉农评此句为"冶铸常识的精准表述"：内壁光洁减少茶味附着、便于清洗，外壁粗糙增大受热面积、耐烧耐用——一锅两性，匠心尽显。

Analysis

The largest gap between Tang and now is that tea was simultaneously medicine, tribute and everyday practice. 吴觉农评此句为"冶铸常识的精准表述"：内壁光洁减少茶味附着、便于清洗，外壁粗糙增大受热面积、耐烧耐用——一锅两性，匠心尽显。 Without that, the chapter collapses into botany.

Conclusion

The section does not give a universal rule. It demonstrates a method: read the text, the annotation and the Tang context together before making a modern claim.

Source: The Classic of Tea, Chapter IV · The Vessels, section 2; the original is in the public domain.

The vessel is not background. 鍑（fù）：煮水的锅。内壁用土模使其光滑易洗，外壁用沙模使其粗糙耐烧。 The same leaf in a different bowl, grinder or sieve changes aroma and texture; vessel and tea are defined together.

Water and fire magnify the difference. The same leaf at a higher temperature or a longer steep changes the sweet-bitter balance; the text only becomes operational at the brewing stage.

Modern tea science would split the sentence into cultivar, soil, light and plucking variables. 吴觉农评此句为"冶铸常识的精准表述"：内壁光洁减少茶味附着、便于清洗，外壁粗糙增大受热面积、耐烧耐用——一锅两性，匠心尽显。 The variables remain useful, but none of them alone explains the cup.