The sponsor used anecdotal evidence to promote a new kiln. (anecdotal: story-based, account-based) One surviving cup supposedly proved its efficacy. (efficacy: effectiveness, efficaciousness, effectualness) A cracked predecessor supposedly proved the old kiln incompetent. (predecessor: forerunner, previous holder, antecedent; incompetent: inept, incapable, unskilled) The potter disputed the logic. (logic: reasoning, rationale, reason) The cup might have been damp, the shelf uneven or the timing wrong.
She placed two cups made from the same clay into each kiln. Her small trial could scarcely settle the question, but it might induce the sponsor to ask better questions. (induce: persuade, prompt, cause) One firing did not exhaust the complexity of the craft. (complexity: intricacy, complexness, complication) The sponsor's promise of infallible results looked increasingly problematic. (infallible: unerring, unfailing, faultless; problematic: troublesome, questionable, difficult)
A week later he returned with an extensive logbook. (extensive: broad, widespread, wide-ranging) His first line recorded an unpropitious start: he had dropped a cup before firing. (unpropitious: unfavorable, inauspicious, unpromising) The potter kept that line. An honest record should make room for events too unhelpful to advertise.