Développement N&B · 2026-09-12

Selenium, Gold, and Sepia Toning: Protecting and Transforming Your Darkroom Prints

The print is done, the paper is dry, you hold it up to the light. It's good. But it could be better — deeper, more permanent, or genuinely different in color. That's where chemical toning comes in. A lot of photographers who develop their own film have never tried it, even though it's the logical next step once you're comfortable making prints.

The principle is straightforward: you replace all or part of the metallic silver in the image with another chemical compound (silver selenide, gold, silver sulfide) that is both more stable over time and a different color. Depending on the product, the dilution, and the paper, results range from barely perceptible to a full, committed color shift. It's neither mysterious nor particularly hazardous if you work methodically. But there are things worth knowing before you drop your first fiber-based print into a selenium bath.

Selenium: the archival workhorse

This is probably the most widely used toner in contemporary darkrooms, and for good reason. Sodium selenite (the active ingredient in selenium toner) replaces silver with silver selenide, a compound that is chemically more stable than pure silver. In practice, that means the print holds up better against oxidation, atmospheric pollutants, and poor storage conditions. This is what's usually called the archival effect.

The most common product is the Harman Selenium Toner (formerly Ilford), sold in one-liter bottles, diluted anywhere from 1+3 to 1+20 depending on the effect you're after. Kodak Rapid Selenium Toner is also available and behaves similarly.

Dilutions and effects

You control selenium toning through dilution and immersion time. There are roughly three distinct ranges:

At 1+19 or 1+20, for 3 to 5 minutes: archival protection only, no visible change. This is the dilution to use if you want to improve permanence without touching the look of the print.
At 1+9, for 3 minutes: a slight cool shift, blacks become marginally denser. On some papers, a faint bluish cast starts to appear.
At 1+3, for 2 to 4 minutes: visible, colored toning. At this concentration you first get an increase in density, then a purplish-violet color develops, more or less pronounced depending on the paper.

Paper type makes an enormous difference. Depending on the silver chloride content, you'll get either a modest contrast boost with minimal color shift, or a clear and obvious toning. A pure bromide paper (like Ilford Multigrade Classic or Fomabrom) responds poorly to selenium in terms of color: the protective effect is real, but even at strong concentrations the color shift stays very subtle. A chlorobromide paper, on the other hand, tones much more readily and more dramatically. RC papers tone too, but the result tends to feel shallower than fiber-based.

Qualitative comparison of visible color shift between bromide and chlorobromide papers as selenium concentration increases. Curves are illustrative — refer to your paper's datasheet.

Safety: take it seriously

The safety data sheet for Harman Selenium Toner lists sodium selenite as the active ingredient. The product can cause skin sensitization. Basic rules: nitrile gloves, good ventilation, and tongs to handle prints — your hands should never go in the tray. Selenium vapors are genuinely toxic, and the tricky part is that selenium doesn't have a strong smell the way sulfur does. The absence of an odor doesn't mean the absence of risk.

Prints need to be properly washed before toning, and re-soaked if they've dried out. After toning, wash thoroughly in running water for 20 to 30 minutes to remove all traces of the solution.

Gold toning: rare, precise, expensive

Gold toning is less common than selenium, not because it's harder, but because gold chloride is expensive and not always easy to source. Bergger Goldtoner is a ready-to-use gold toning solution that can be used straight, after bleaching, or in combination with another toner.

Used with chlorobromide papers, gold toning produces a bluish cast that appears first in the highlights. It's not a garish blue — it's subtle, slightly cool, with a quality that's quite different from selenium. Neutral or cool-tone papers tend to give blue-gray tones.

Gold toning is also used after sepia toning (bleach and sulfide), in which case you typically get a warmer, more blood-red tonality depending on the paper and the sepia bath used. It's a combination technique that experienced printers use to reach results that neither toner could produce on its own.

Like selenium, gold salts also improve the long-term stability of silver prints. The cost reflects the chemistry: gold chloride is a precious and genuinely scarce material.

Sepia toning: two baths, one warm result

Sepia is the oldest of the three, and probably the most visually evocative. It gives prints an amber, warm tone associated with early twentieth-century photography. It also improves image permanence, because silver sulfide is chemically more stable than metallic silver.

The standard process uses two baths:

Bleaching: immerse the print in a potassium ferricyanide and potassium bromide solution until the blacks disappear and you're left with a pale yellow ghost image. The potassium bromide speeds up the bleaching and "cools" the final tone. You can bleach completely or partially. For partial bleaching, working with a weaker dilution gives you more time to pull the print before the shadows are gone. It's a useful technique: by stopping before the blacks fully disappear, you preserve deep shadow detail and limit the toning to midtones and highlights.
Sulfiding: after rinsing in clean water (until the yellow tint is gone), the print goes into the sulfiding bath, which converts the bleached silver back to amber silver sulfide. Two options here: sodium monosulfide baths, which are effective but produce a strong smell, or thiourea (combined with sodium hydroxide). Thiourea is odorless, which makes it a much more practical choice for working at home.

Sodium monosulfide smells strongly of rotten eggs and requires serious ventilation. For apartment use, thiourea is the obvious answer. You can also buy ready-to-use products like Fotospeed ST20, a sepia toner diluted 1:19 that comes with an additive for adjusting the final tone. It's a solid starting point when you'd rather not weigh out chemicals from scratch.

The two-bath sepia process: bleaching converts silver to a pale ghost image; sulfiding converts it to warm amber silver sulfide.

How paper affects the result

Sepia works well on fiber-based paper, though it also gives decent results on RC — the image just takes longer to bleach out. The final tone on RC tends to be slightly less warm than on fiber, and the depth of rendition isn't quite the same. For a really satisfying sepia print, fiber-based is still the reference.

The paper choice matters from the start. A warm-tone paper will give you an amber, almost golden-brown sepia. A neutral or cool-tone paper will produce a grayer, sometimes almost beige result. It's no coincidence that printers who work seriously with sepia often start with warm-tone chlorobromide paper.

A few principles that apply across all toners

Whatever toner you're working with, some rules come up every time.

The print must be properly fixed and washed before any toning. Incomplete fixing or insufficient washing leads to uneven results, sometimes with staining. Dry prints should be soaked in water for a few minutes before you begin.

Manufacturer times are starting points. In practice, bath temperature, solution age, and paper type all shift the results. Working by eye is usually more reliable than following a timer blindly, especially for selenium and sepia.

Then there's print density. For selenium, print slightly lighter than normal because toning increases shadow density. For sepia, do the opposite: the bleaching step reduces density before the sulfiding bath brings it back, so you want to start a bit denser to compensate. It's worth making test prints with exposure times reduced by 10 to 20% (for selenium) or increased (for sepia). You'll dial it in quickly once you understand what's happening.

Going further

If you want to get started without overcomplicating things, Harman Selenium Toner at 1+19 is an ideal entry point: no visible change, just permanence, and you get used to the workflow (gloves, washing, tongs) before moving to stronger dilutions. Fotospeed ST20 is a similar low-friction option for sepia: the kit is simple, the additive lets you tune the tone, and you're not weighing thiourea your first session. For gold toning, Bergger Goldtoner is the most accessible reference; try it on work prints on chlorobromide paper before committing your best prints. Worth reading: Ilford's technical data sheets on the permanence of fiber-based prints lay out clearly why selenium toning extends print life, with actual test data to back it up.