Also known as: Yang Metal · Sword Metal · Iron
Geng is yang metal, classically the war-axe and the autumn frost (劍戟之金). It severs what cannot remain, executes the harvest, ends one cycle to allow the next. Geng Day Masters carry an air of sharpness and decisive action — natural law-enforcers, soldiers, judges, surgeons. They prefer truth over pleasantness and respect strength.
Geng pairs with 乙 in 乙庚合化金 — yang metal courted by yin wood, the soft tempering hard. Geng requires fire to refine it into a tool (火煉真金) and water to wash off rust; Geng without fire stays raw iron, never becoming a precise instrument.
For a Geng Day Master, begin with the month. Shen (申 shēn) and You (酉 yǒu) give it seasonal command; heavy earth feeds it to the point of burial; fire turns it into a finished tool. The point that Geng must be forged before it becomes a vessel is made above, and one layer needs adding to it: the most quoted judgement is that Geng prefers Ding (丁 dīng) to Bing (丙 bǐng), because Bing is sunlight, which illuminates without melting, while Ding is the furnace flame that forges. So whether Ding appears among the stems, and whether it has wood for fuel, often matters more than the sheer quantity of fire. A weak, rootless Geng in blazing fire is injured instead of refined, and the reading then shifts to earth support or companion stems.
The axe came later. When Han commentators explained the seventh stem they reached for a pun, tying Geng (庚 gēng) to geng (更), to change over, the hinge where autumn turns growth into gathering. Shuowen Jiezi (說文解字 Shuōwén Jiězì) places it in the west and reads it through the image of crops standing full. The war-blade imagery that dominates modern descriptions is a secondary layer, a way of picturing that decisive cut. It is useful, but it is a metaphor, and a chart reader should not mistake the picture for the thing.
Three habitual misreadings follow from that confusion of picture and thing. The “killing” quality attributed to Geng is routinely taken for cruelty, when in classical usage it describes a seasonal function — harvest, closure, the end of a cycle — and carries no verdict on character or fortune. The second equates the metal element with literal metal; what the tradition means is the process of contraction and decisive cutting, with metal objects supplying the image. The third involves the sound-element layer: each sexagenary pair carries its own nayin (納音 nàyīn) element, so the Geng-Wu pair is classified as roadside earth there, which does not contradict Geng being metal as a stem.
Geng and Xin (辛 xīn) are both metal but read in opposite directions: one is ore that improves with forging, the other a finished object that resents the furnace. Geng controls Jia (甲 jiǎ) wood — Seven Killings to a Jia Day Master, Indirect Wealth to a Geng one. An older technique reads the pair as splitting timber into fuel so that Ding fire can burn, a three-stem chain and not a single control relationship. With Yi (乙 yǐ) wood, Geng forms one of the five stem combinations, which the old manuals named for benevolence and duty: hardness meeting softness and accepting a limit.
Geng's growth-stage position is one of the tradition's noisiest disputes. The standard twelve-stage table runs yang stems forward and places Geng's birth stage in Si (巳 sì), a branch that hides Bing fire, which controls metal. How metal can be born in a fire place has been asked for centuries. One camp keeps the table and points to the Geng concealed inside Si as the seed; another argues that yin and yang stems share a single cycle, or simply treats Shen as metal's real seat of strength. No consensus exists, so when two charts disagree, check which table is in use before arguing about the verdict.
Put Geng back into the solar calendar and it reads more clearly. From Start of Autumn (立秋 Lìqiū) metal takes command, the Shen month belongs to it, and the year turns from raising things to gathering them in. Phenological almanacs such as the Yueling Qishi'er Hou Jijie (月令七十二候集解 Yuèlìng Qīshí'èr Hòu Jíjiě) record exactly that shift from abundance to austerity. Classical writers extended the pattern to human affairs, describing Geng-dominated periods as fit for settling accounts, deciding matters and completing what was begun, and unsuited to opening something new.
Because the tradition pictures Geng as unrefined ore that only becomes a usable tool after forging, and fire does the forging. Ding fire is usually preferred to Bing: a furnace melts, whereas sunlight merely warms. The rule carries a condition, though — a strong, rooted Geng can take the heat, while a weak rootless one facing blazing fire is simply damaged, and classical practice then turns to earth support or companion stems instead.
Geng is yang metal: raw iron, the axe, the unfinished blade, direct and decisive. Xin is yin metal: worked gold, ornament, fine instruments, precise and particular. The most practical test is their attitude to fire. Geng wants the furnace because forging completes it; Xin has already been through fire and loses its finish if sent back. Polarity says nothing about strength, which still depends on the month branch and on roots.
No. The severity attached to Geng describes an autumn function in classical language — cutting the harvest, closing out what is finished — and is a neutral process description rather than a judgement on character. Geng Day Masters are traditionally described as decisive and principled, qualities that read as executive strength in one configuration and as rigidity in another. Judging temperament from the day stem alone is not how classical charts are actually read.
That objection is precisely what the tradition argues about. Following the yang-forward twelve-stage table, Geng's birth stage does fall in Si, and defenders point to the Geng metal hidden inside that branch as the seed. Critics reply that Si is a fire place and that a birth stage there is incoherent, preferring a shared yin-yang cycle or treating Shen as metal's true seat. Both systems remain in use, so identify the table before comparing results.
Unchecked metal is described as heavy or cold, and the usual imagery is something too rigid to bend. Two remedies are traditional: fire, which forges the surplus into something usable, and water, which drains it so the metal flows outward instead of piling up. Which one is chosen depends on seasonal warmth — autumn and winter charts are already cold and usually take fire first, while summer charts already carry heat and lean on water.