Sensitizer Trials — Cyanotype Coating Solution¶

Status: OPEN — trials required before the chemistry bulk order is finalized.

The per-print cyanotype sensitizer recipe is not yet pinned down, and the unknowns have a large effect on the chemistry budget and the number of prints a given order yields. This page lists the trials needed to lock the operating manual §0.2 / §0.3 / §2.1 recipe and the master shopping list / cost breakdown quantities.

These can be run post-construction at full scale, or — preferably first — on the TBS-002 proof-of-concept at small scale to converge cheaply before mixing kilograms of chemistry.

Why this matters (not a rounding error)¶

The active image plane is 4,499 × 2,388 mm = 10.74 m² and is coated two wet-on-wet coats (§2.5). The per-print chemistry therefore scales as coverage (ml/m²) × 2 coats × 10.74 m² × concentration. Two of those terms are estimates:

Coverage (muslin absorption): sourced at ~120 ml/m²/coat for cotton (AlternativePhotography / Ruth Brown: medium cotton 140 ml/m of 114 cm = ~123 ml/m²; cross-checked against Jacquard: ~473 ml over ~50 8×10 fabric prints = ~183 ml/m²) — but not yet measured on our actual pre-washed muslin. Plausible range ~100–180 ml/m²/coat.
Concentration: Ware New Cyanotype is 30 g AmFe : 10 g ferricyanide : 0.1 g ammonium dichromate per 100 ml — but that strength is for rod-coated paper (29 ml/m²). Applied at fabric volumes it over-deposits ~8× the paper chemistry density, so fabric work runs Ware's 3:1 ratio at a diluted strength. How dilute (and still give adequate Dmax) is the open question.

Impact: these two unknowns set the chemistry order size directly. For the 50-print run the AmFe order swings ~3× across the concentration tiers (Lean ⅓-Ware → Rich full-Ware), and coverage is still unmeasured on our muslin, so the real yield could sit further off still. The per-tier masses and their cost band live in the operating-manual §0.2 table and the cost breakdown; the trials below pin which tier applies before the bulk order commits.

Trials¶

T1 — Muslin absorption / coverage rate¶

Goal: measure ml/m² per coat on the actual substrate. - Pre-wash the production muslin twice (remove sizing, per chemistry-shopping-list §5). - Mount a 1 m² test piece. Weigh the sensitizer container before and after a single controlled brush/roller coat; mass ÷ density (~1.05 g/ml) = ml applied. - Repeat for the second wet-on-wet coat and record the combined ml/m². - Output: confirmed coverage (replaces the ~120 ml/m²/coat estimate).

T2 — Concentration vs density (the cost driver)¶

Goal: find the leanest strength that still gives full shadow density, to avoid wasting chemistry. - Mix three strengths at Ware's fixed 3:1 ratio: Lean ⅓-Ware (10 g AmFe/100 ml), Standard ½-Ware (15 g/100 ml), Rich full-Ware (30 g/100 ml). - Coat, expose identically (step wedge), develop, and read Dmax / tonal separation. - Output: the production concentration tier → fixes per-print AmFe/ferricyanide.

T3 — Ammonium dichromate contrast level¶

Goal: set the contrast agent for the scene/negative contrast without excess fog/stain. - Vary dichromate 0.1% (baseline) / 0.2% / 0.4% of the working volume on otherwise identical coats; expose and develop a step wedge. - Output: the production dichromate % (Ware: "increase for more contrast").

T4 — Single vs double coat¶

Goal: confirm two wet-on-wet coats are needed (vs one) for even density on muslin. - Compare a single coat against two wet-on-wet coats at the chosen strength. - Output: confirm or revise the ×2 coat assumption (halves/doubles the per-print volume).

T5 — Exposure calibration at the locked recipe¶

Goal: baseline exposure time in full sun once T1–T4 fix the recipe (feeds operating-manual §3.1).

Acceptance / sign-off¶

A tier and dichromate level are "locked" when T2/T3 show acceptable Dmax + contrast on the production muslin, and T1 fixes the coverage. On sign-off, cascade the numbers into operating-manual §0.2/§0.3/§2.1, the master shopping list, and the cost breakdown, and mark this page CLOSED with the chosen values recorded.

Source References¶

AlternativePhotography — Cyanotypes on Fabric: Preparing the Fabric (Ruth Brown) — fabric coverage rate (~123 ml/m² on medium cotton).
Jacquard Cyanotype Sensitizer Set (Dick Blick) — coverage cross-check (~183 ml/m² over ~50 8×10 fabric prints).
Mike Ware — The New Cyanotype Process — AmFe sensitizer chemistry, the 3:1 ratio, and dichromate contrast control.