Lumen-Stone

Lumen-Stone is the collective designation for any mineral body that retains, emits, or accounts for light in a manner recognised by the Lumen Regulation Bureau. The term is administrative rather than geological: a stone is Lumen-Stone when the Bureau says it is, and the Bureau's position on the matter has been revised eleven times since the designation was first struck. Ordinary quarried rock, however bright, is not Lumen-Stone. A grey and unremarkable cobble that has been entered in a Taxonomic Lumen Ledger is.

Definition and measurement

Lumen-Stone is quantified in Standard Lumen Units against the Standard Lumen held under seal by the Bureau. Retained light is measured by enclosing the specimen in a darkened cabinet of fixed interior volume, withdrawing it after a stated interval, and reading the residual glow against the reference standard. Emitted light is measured the same way, with the cabinet door left open. The method is set out in Second Concordance, Annex 7, which advises that "the cabinet be swept between specimens, as dust carries a charge."

A specimen that measures below one-tenth of a Standard Lumen Unit is classed as Inert and struck from the ledgers without ceremony. This threshold has been challenged repeatedly by the Quarrymen's Benevolent Association, whose members argue that the Bureau's cabinet is simply too large. The Bureau has declined to change the cabinet. It is a fixed cabinet, purchased in the reign of the sixth Archivist, and the Bureau has stated in writing that it does not intend to purchase another.

Lumen-debt and the Kael settlement

Because Lumen-Stone retains light drawn from its surroundings, the Bureau long held that every luminous specimen carried a debt: light borrowed from the general supply and owed back to it. Extraction of a luminous body without settlement of its debt was treated as an unlicensed withdrawal, a position formalised in the Edicts of the Unyielding Stone and administered under the Lumen Synthesis protocol.

This doctrine was broken by the ruling of Grand Luminist Kael, who found that certain naturally luminous formations — chiefly those in which the glow appeared to originate within the stone rather than to have been drawn into it — constituted a taxonomic anomaly and carried no lumen-debt at all. The Bureau has never fully accepted the ruling, and its recensions of the Ledgers still annotate Kael's specimens with a marginal sigma. When asked what the sigma denotes, the Bureau's clerk of records, Orvin Pell, replied that it denotes the marginal sigma. The enquiry was not pursued.

Lumen-Stone and Living Stone

Lumen-Stone is frequently confused with Living Stone, the spontaneously animate stone manifestations catalogued elsewhere in the archive. The two classifications are distinct in principle and frequently inseparable in practice. A luminous formation that shifts its outline between measurements is a question for the Provisional Stone-Wardens Committee, which shares governance of such deposits with the Corridor Wardens; a formation that merely glows is a question for the Bureau. Where a specimen does both, the Wardens and the Bureau exchange letters for an average of fourteen months before one of them measures it again.

A notable instance is Basalt of Stillness, a form of Living Stone that emits no measured light but retains an unaccountable quantity of it. The Bureau has classified the Basalt as Lumen-Stone on the grounds of retention, while the Wardens classify it as Living Stone on the grounds of stillness. No specimen of the Basalt has been permitted to leave the floor on which it was found, though it has been measured there twice.

The Silent-Stone exclusion

Light-carrying stone that has ceased to carry light is not Lumen-Stone under current practice, whatever its previous classification. The position is complicated by the Silent-Stone of which the Foundation Stone is composed. Silent-Stone carries no light and has never been shown to have carried any, but the Third Concordance opens with the line "all stone from which the Tower's light has gone out is Lumen-Stone at rest," a formulation drafted in a different century and never revised. The Bureau's reading is that the clause is decorative. The Office of Recensions has declined to rule on whether a decorative clause is binding, on the grounds that ruling on it would make it not decorative.

Attempts to reconcile the two positions have been filed, numbered, and shelved. The filing clerk, Merrin Vale, appended a note in 4 Y.I. observing that "the matter has been settled four times and the settlements do not agree," and withdrew from correspondence on the subject thereafter.

Incidents

The best-known incident involving Lumen-Stone occurred on the eighth floor in the winter of 17 Y.I., when a consignment of measured specimens was found to have gained light in transit. The gain was small — nine specimens had each acquired roughly a quarter of a Standard Lumen Unit — but the Bureau treated the matter as a treasury breach and sealed the stairhead for eleven days. The carrier, Halvard Cruse, maintained that the crates had been stacked beside a lit sconce. The Bureau's finding was that the crates had been stacked beside a lit sconce. Neither party regarded this as an explanation.

Regulation followed. Under Fourth Concordance, Annex 2, Lumen-Stone in transit must be conveyed in lined boxes and must not be stored within one pace of an attenuated lumen-sconce, a lit window, or a reflective surface. Cruse was fined the value of the gained light at the current rate. He paid in coin, which the Bureau does not accept for lumen assessments, and the coin was returned to him the following spring.

Scholarly dispute

There is no agreement on whether Lumen-Stone is a natural category or a bookkeeping convenience. The Bureau's formal position, stated in the preamble to every recension of the Ledgers, is that the classification "follows the light and not the ledger." Against this, the Seventh Concordance provides that a stone's classification is determined by its entry, and that a mislaid entry is not an error of classification but a loss of it. The two documents have stood side by side for a very long time and are cited alternately, according to which settles the dispute at hand.

"Where the ledger and the stone disagree, the ledger is nearest to hand."

— Seventh Concordance, Clause 3

The practical consequence is that a Lumen-Stone with no surviving entry is treated as unclassified rather than as ordinary rock, and may not be quarried, purchased, or knowingly walked past. The Bureau maintains a corridor of such specimens on the fourteenth floor, unfiled and gently aglow, which visitors are asked not to count.