Viscosity Assay

The Viscosity Assay is the standing procedure by which the Tower determines whether a given substance is one thing or several things, by measuring the rate at which it resists its own movement. It is administered jointly by the Office of Assay and the Registry of Assay, and its results are recorded in the Assay Rolls, a continuous series maintained on Floor 3,117 since at least the fourteenth recension. The Assay is the Tower's principal instrument of distinction: where Interlocutory Ruling 88 holds that a distinct designation implies a distinct substance, the Viscosity Assay is the means by which distinctness is demonstrated when no other means will serve.

The procedure is not, as is sometimes supposed, a test of thickness. It is a test of coherence. A substance that resists flow uniformly is held to be one substance; a substance that resists flow unevenly, or resists it differently at different depths or under different seals, is held to be a compound requiring further assay, further designation, and — in the ordinary course — an amendment to some earlier ruling.

Method

Assay is conducted in a standard vessel, the assay cone, of which four hundred and nine are held in the Registry's stores. The cone is filled to the third mark and drained through a calibrated aperture under the provisions of the Manual of Hydrographic Protocol, Annex 9. The time of drainage is recorded against a reference series derived from Liquid Ambivalence, whose behaviour under assay is considered exemplary. Cross-applicational checks are performed with the Oneiroscone, sanctioned for the purpose under Amendment 47-Θ.

Where a substance cannot be drained — because it does not flow, or because it flows only when unobserved, a condition noted in eleven cases on Floor 2,880 — the Assay proceeds by indentation, and the result is entered with the qualifier reluctant. Reluctant results carry the same authority as ordinary ones but are assayed in the morning.

History

The Assay in its present form descends from the emergency procedures of the Great Viscosity Event, first recorded at Aperture Beta in the winter of Year 14,722. During that period the Office of Descent Hygiene issued a provisional ruling requiring outbound inventories to be tagged with a Viscosity Seal of the Third Mark, a requirement never rescinded and now observed chiefly by habit. The findings of the period were principally memorialised in The Principle of Procedural Viscosity, whose administration was later assigned to the Calibration Bureau. Clause 44.2 of the Codicil on Ink Viscosity traces its numbering to an assay anomaly in the same winter and not, as is often repeated, to the number of the floor on which the anomaly occurred.

The modern assay schedule was fixed by the Tenth Concordance, which also governs the custody of Wishful Cypress and, by extension, the assay of any substance that behaves like it. Where a material resists assay altogether, the Office of Assay may issue a standing annotation of the kind maintained for Alloy Γ-9 — "non-reactive; constituents as sealed" — which closes the matter without resolving it. Archival Alloy 7b continues to be handled under a similar annotation renewed each year, and Sigma-Glass Precursor is assayed under the separate arrangements of Sigma-3 along Line Sigma. The relationship of Sigma-9 to the Line Sigma series remains the subject of a standing query at the Registry.

The Viscosity Slate

Results are entered on the Viscosity Slate, a slate tablet of the Registry's own manufacture, in a dark ink whose viscosity is itself specified: not less than twenty-two seconds in the standard cone at Season Hall temperature. The specification descends from Clause 44.2 of the Codicil on Ink Viscosity, and its enforcement has occasioned more disputes than any other part of the Assay.

The difficulty is that the ink must be assayed before it can be used to record an assay, and the ink used to record that preliminary assay must itself be assayed. The Tower resolved this regress by the Third Concordance, which permits the first entry of any Roll to be made in pencil. Clerks of the Registry refer to this as the concession, and it is the only pencil permitted in the Assay chamber.

Dispute: the status of the Seal

A long-running disagreement concerns whether the Viscosity Seal of the Third Mark certifies the substance or merely the inventory. The Seventh Edict of Floor 1004 takes the stricter view, that the Seal attaches to the goods themselves and travels with them; the Registry of Assay has maintained since the Fivefold Assay that the Seal attaches only to the line in which the goods are listed. The consequence is practical. Under the Edict, a barrel of assayed resin moved from Floor 1004 to Floor 1005 must be re-sealed at the stairhead. Under the Registry's reading it must not.

Matters came to a head in the winter following the Fivefold Assay, when the surveyors who had fixed the boundaries of the Desiderata Precinct returned to find their own reference carboy sealed twice — once by the Edict's officer and once, independently, by a Registry clerk named Halvard Nimm, who had been stationed at the stairhead for nine years and had his own views. Nimm's objection, entered in the margin of the Assay Roll in a clear hand, was that the second seal implied the first had been insufficient, "which the first seal, being a seal, cannot be". He was reassigned to the Scriptorium Supply Ledgers the following spring and continued to enter the objection there for a further eleven years, in the ink column, where it was eventually noticed.

No Concordance has settled the question. The Lexicon of the Lower Stacks notes only that both readings are in good standing and advises travellers between floors to carry a spare seal and a written explanation.

Recorded anomalies

The Assay Rolls record a small number of results that the Registry has declined to classify, listed here as they are entered in the Roll:

• The Wick Reversal — three cases, Floor 6,042, in which a substance assayed slower after warming.
• The Stonewater Entry — a single line, Floor 3,118, recording a result of "n/a, and correctly so".
• The Aldermoor Return — a sample that assayed identically in six consecutive years and then, in the seventh, assayed as a different substance of the same name.

The Aldermoor Return remains open. The Registry's standing note on the file observes that the substance was not lost, mislaid, or altered in custody, and that the Assay has therefore done what it was asked to do.