Ola Senn turns the old copper weight toward the lamp before the first assay. A shallow notch remains where a maker’s mark once distinguished it from the weights used by the guild tables. The stamped measure is still legible; the hand that made it is not.
The challenge book gives the dispute a practical shape. Guilds say a single standard hides differences in bar shape that matter when copper is carried to a furnace. Buyers say separate certified weights make it harder to compare one bar with the next. Both sides agree that the notch has worn smooth; they disagree about what should replace it.
Senn’s table checks bars against the common weight and records any challenge. The slips do not show whether a second guild weight would improve a buyer’s comparison, because the same bar has not yet been tested under both systems on the same day.
The assayer keeps a small cloth under the weight so the brass does not ring against the stone. She says the sound tells her when a bar has shifted, but the number in the book is what a buyer can take away. A standard has to be repeatable by someone who was not present for the weighing.
The table is preparing a paired test of the common and guild-certified systems. For now, copper changes hands under the old weight, with the challenge book open beside it.
