HC-110, introduced by Kodak in 1962, is a liquid-concentrate black-and-white film developer whose nomenclature confuses more often than it clarifies. The concentrate is a thick, honey-like syrup, and the published development times are keyed to a series of single-letter dilutions: A, B, C, D, E, and F. Two further letters, G and H, circulate widely but appear in no Kodak publication; they were defined later by users. The reference datasheet is Kodak Alaris Publication J-24, dated December 2017, and reading the letters correctly means keeping two distinct measuring points apart: the raw syrup, and an intermediate stock solution mixed from it.

The Two Measuring Points

HC-110 can be mixed either directly from the syrup or by way of a stock solution. The stock solution is made by diluting one part concentrate with three parts water, a 1:3 mix; J-24 states the reason plainly: “Due to the high viscosity of the developer concentrate, it is preferable to dilute it to a stock solution.” The honey-thick syrup is hard to measure accurately in the small volumes a single roll needs, and the thinner stock pours and meters cleanly. Kodak advises a graduated cylinder accurate to 0.5 mL, or a positive-displacement syringe, when measuring concentrate directly, and notes that working solutions may be mixed anywhere from 10 to 32 C (50 to 90 F).

The single 1:3 figure describes only that stock. The lettered working dilutions are not all mixed from the same uniform scheme; each letter has its own ratio, and the figure differs depending on whether you start from concentrate or from stock. J-24 gives both tables, and states that the two routes “provide the same photographic characteristics”:

Dilution	From concentrate	From stock
A	1:15	1:3
B	1:31	1:7
C	1:19	1:4
D	1:39	1:9
E	1:47	1:11
F	1:79	1:19

The lettering is not a descending strength ladder. Read the concentrate column and C, at 1:19, is stronger than B at 1:31; only the alphabetical order suggests otherwise. The letters are labels, not a sequence. Several were chosen to reproduce the activity of older Kodak products: dilutions C, D, and E were designed to match the sheet-film times of DK-50, DK-50 1:1, and DK-50 1:2 respectively (1:19, 1:39, and 1:47 from concentrate), so a photofinishing lab switching from DK-50 could keep its existing time charts. HC-110 was first marketed to black-and-white photofinishers running automated equipment, and the lettered structure carries that origin.

Why Dilution B Became the Hand-Processing Default

Dilution B, 1:31 from the syrup, settled in as the reference strength for general small-tank hand work because its activity places common films in a controllable time window. J-24’s roll-film table, at 20 C (68 F) with manual agitation at 30-second intervals, gives Tri-X Pan at 7.5 minutes in B, T-MAX 400 at 6 minutes, and Plus-X at 5 minutes.

The floor under those figures is Kodak’s own rule, stated verbatim in J-24: “Tank-development times shorter than 5 minutes may produce unsatisfactory uniformity.” Below five minutes the pour-in and pour-out intervals become a large fraction of the total and any agitation error is amplified across too little time. Dilution A makes the problem concrete: the same Tri-X that needs 7.5 minutes in B drops to 3.75 minutes in A, well under the uniformity floor. That is the practical reason B, not the stronger A, is the standard for processing by hand.

Two Levers on Contrast, Not One

Greater dilution does lengthen development and moderate highlight density, but it is easy to overstate it as the only contrast control. J-24 keys its times to printing on normal-contrast paper with a diffusion or contact enlarger, then adds a separate process lever: “If printing negatives with a condenser enlarger, decrease the development time by approximately 30 percent to produce lower contrast.” A condenser head raises printed contrast through the Callier effect, so the negative is developed less to compensate. Dilution and development time are one pair of controls; the enlarger type is another, and the two interact.

Finite Capacity and the Compensating Effect

The useful anchor for the whole capacity argument is a single number: roughly 6 mL of syrup is needed to develop one 135-36 cassette, one 120 roll, or one 8x10-inch sheet to completion, and that active quantity is the same regardless of which lettered dilution you mix it into. A one-shot at high dilution simply spreads that fixed 6 mL through a larger volume of water. Push the film area too far, or use a dilution so weak it carries too little syrup for the load, and the developer exhausts locally over dense, heavily exposed areas before the thin shadow areas finish.

That local exhaustion is the mechanism behind compensating development. Ansel Adams used highly dilute HC-110 for exactly this, holding highlights while shadow detail built; he describes it in The Negative (2002 reprint, p.226), working Tri-X Professional in dilute HC-110 for roughly 18 minutes at 20 C (68 F) with a pre-soak. His governing principle is that a highly dilute developer behaves like the same developer at normal strength if the time is extended enough and agitation is normal, provided the normal amount of stock developer is present in the dilute solution. The compensating effect appears only when agitation is reduced: continuous agitation for the first minute, then about 15 seconds every three to four minutes, lets developer sit and exhaust over the highlights while the shadows keep working. The unofficial dilution G (1:119 from syrup) and the “1+90” figure are associated with this technique.

Where G and H Come From

Neither G nor H appears in any J-24 table; both were defined by users for specific jobs. Dilution H is conventionally 1:63 from syrup, half the strength of B, a convenience strength for stretching times slightly or for thinner emulsions. Dilution G, conventionally 1:119, is the high-dilution compensating and high-acutance strength of the kind Adams used. Knowing they sit outside Kodak’s tables matters: there is no Kodak time chart for them, so times must be found by testing rather than read off a datasheet.

The two-stage scheme earns its keep through shelf life. The concentrate’s keeping properties are exceptional; sealed full and small, the syrup will keep at least four years and routinely outlasts its printed expiry, while a mixed working dilution is short-lived once water is added. Decanting the syrup into completely full, tightly sealed small glass bottles keeps air out and preserves it. Read against the syrup it descends from, the lettered system is finally a shorthand for one decision: how much developing agent reaches the film.