A single sheet of MULTIGRADE RC DELUXE can print a flat negative at grade 5 and a harsh one at grade 0, with nothing changed but the colour of the enlarger light. That flexibility replaces the boxes of fixed-grade paper a darkroom once needed, and it rests on a specific piece of emulsion engineering. The paper carries three light-sensitive components, each tuned differently to green, and the colour balance of the printing light selects between them. Understanding how those three components respond explains both how a grade is chosen and why exposure does not stay constant across the range.

Three emulsions in one coating

All silver chloro-bromide printing emulsions are inherently sensitive to blue light, with only slight sensitivity to green. Variable-contrast paper exploits this. According to Ilford’s technical sheet Contrast Control for ILFORD MULTIGRADE Variable Contrast Papers, the coating is not a single emulsion but a mixture of three separate ones — the curve diagrams label them dyed emulsions I, II and III. Each is the same basic blue-sensitive emulsion carrying a different amount of green-sensitising dye: one part responds mainly to blue, one to blue plus some green, one to both blue and green strongly. All three share the same inherent contrast and the same speed to blue light. They differ only in their green speed.

That single asymmetry is the whole mechanism. Expose the paper to blue light and all three emulsions react together at the same speed; their characteristic curves coincide and stack, summing to a steep curve with a narrow exposure range — high contrast. Expose it to green and the three respond at markedly different green speeds, so their curves shift horizontally relative to one another. The sum of three displaced curves has a much shallower slope: a wide exposure range, low contrast. Every grade between the extremes is just a different proportion of blue to green reaching the emulsion.

Setting the grade with magenta and yellow

The colour balance is set by filtration. A magenta filter absorbs green and transmits blue, pushing toward the high-contrast blue response; a yellow filter absorbs blue and transmits green, biasing toward the soft green response. Ilford’s MULTIGRADE filter set runs to twelve filters numbered 00 to 5 in half-grade steps, the lowest number being the softest. These hand filters are deliberately tinted to a semi-neutral density so that the printing time stays constant across most of the range: filters 00 to 3½ all hold the same exposure, and 3½ is the last grade that does so.

Past that point exposure jumps. Ilford’s wording is exact — the exposure time for filters 00 to 3½ is the same; that for filters 4 to 5 is double. The 2× factor is not arbitrary. At grades 4 and 5 the heavy magenta filtration starves the paper of usable green, leaving it to lean almost entirely on the slow blue-only component, so it needs roughly twice the light to reach the same density. The filter design and the exposure shift are the same fact seen from two ends.

Reading the grade off the negative

Grade selection need not be guesswork. Ilford grades each paper by its ISO Range, R, under ISO 6846:1992 — the log-exposure range of negative densities the grade will print onto the full paper scale. A higher R figure means a wider negative range accommodated, which is a softer grade. For the current MULTIGRADE RC DELUXE the figures run grade 00 = 160, 0 = 130, 1 = 110, 2 = 90, 3 = 70, 4 = 60, 5 = 50, with no filter sitting at about 90. (The discontinued MULTIGRADE IV RC DELUXE ran softer and harder at the ends: 00 = 180 down to 5 = 40.)

To use these, measure your negative’s effective density range on the baseboard with an enlarging meter, multiply the log range by 100, and match the nearest R figure. Ilford’s own worked example: a negative with an effective density range of 1.32 log exposure units gives 1.32 × 100 = 132; the nearest published figure is 130, which on MULTIGRADE RC DELUXE corresponds to grade 0. Print at that grade and the negative’s full tonal range maps onto the paper’s. The same negative on the old grade 0 (R = 160) would have printed flat, which is why the R table belongs to the specific paper, not to the grade number alone.

Setting the grade on a colour head

A dichroic enlarger dials the same balance in yellow and magenta. Ilford publishes per-head tables; for a Durst head with a maximum of 170M, the single-filter settings run grade 00 = 150Y, 0 = 90Y, 1 = 55Y, 1½ = 30Y, grade 2 = 0/0, 2½ = 20M, 3 = 45M, 4 = 100M and 5 = 170M. Kodak and Meopta heads need different numbers from the same table. A dual-filter method — for the Durst, grade 00 = 115Y/0M, 2 = 52Y/20M, 3 = 34Y/45M, 5 = 0Y/170M — calls for longer exposures but needs less re-dialling when you change contrast mid-session.

One limitation to know before chasing maximum contrast on a colour head: dichroic filters are optimised for colour paper, not VC paper, so the hardest grade a colour head can dial in is slightly lower than a true grade-5 hand filter delivers. Ilford states this plainly and treats all the suggested filtration tables as a starting guide to confirm by test strip, not as gospel.

Light source matters

Every figure above — the constant-exposure behaviour, the 2× shift, the filtration tables — assumes a tungsten or tungsten-halogen lamp. Other sources break those assumptions. With an Aristo W45 cold-cathode head, Ilford recommend dialling in an extra CC40Y to recover the full contrast range; even then the grade intervals bunch toward the hard end, and exposures must be recalculated when you change grade. Their factor table for MULTIGRADE IV RC DeLuxe on that head shows a print made at filter 2 needing its time multiplied by 0.74 to print at filter 3 — the opposite-direction shift to what a tungsten head would give. Modern LED VC heads, with their separate blue and green channels, behave differently again and carry their own calibration.

A note on history, and how it is used

Ilford announced Multigrade in 1940 as the first variable-contrast paper of its kind, narrowly behind Defender’s Varigam of 1939. The three-emulsion design is not original to it: the earliest variable-contrast papers used two emulsions — one high-contrast layer sensitive to blue, one low-contrast layer sensitised to green — and the green-dye-graded three-emulsion mixture came later. The architecture changed; the principle of trading blue against green did not. Foma Fomaspeed Variant, Adox MCC and MCP, and Kentmere VC all work the same way today.

In practice the paper is undemanding. MULTIGRADE RC has roughly uniform spectral sensitivity across the range and an ISO paper speed equivalent to a film of only ISO 3–6, so it tolerates a standard safelight — the ILFORD 902 light-brown filter is the one recommended for it — used no closer than 1.2 m and not for direct exposure beyond four minutes. Develop in ILFORD Multigrade developer, a Dimezone-S and hydroquinone PQ-type liquid concentrate, at the normal 1+9 dilution (or 1+14 for more control and economy): RC paper clears in 60 seconds at 20°C, fibre-base around two minutes.