In 1910, the Berlin Aniline Works — the American arm of the German chemical giant that would soon become a household name through Agfa film — published a slim handbook of darkroom recipes. Edited by George L. Barrows, it was meant to settle the recurring complaint that customers blamed defective plates for what was, in fact, defective developing technique. Tucked into the introduction is a piece of practical wisdom that has almost entirely vanished from modern memory:

Pinholes or minute white specks are very common, and are caused by small particles of dust settling on the plate or film while it is being handled in loading the plate holder, making the exposure, or developing, the developer thereby being prevented from properly acting upon the sensitive film.

That much survives in modern photographic lore. But Barrows continues with a tactile remedy that most photographers under fifty have never heard of:

Small white spots of clear gelatine are due to air bubbles that cling to the surface of the film when in the developer, and prevent the solution from acting upon that particular place. They should be instantly removed with the finger or a soft brush by rubbing lightly the plate or film.

Read that again: rub the wet, light-sensitive emulsion with your finger. To anyone raised on the modern dogma that you must never, ever touch a negative — that fingerprints are forever, that even cotton gloves are barely safe — this advice sounds reckless. Yet it was completely standard practice. The gelatine emulsion, while soft and swollen in developer, is also surprisingly forgiving; the bubbles cause a measurable defect (the "clear gelatine" white spot), while a quick brush of the fingertip causes none at all, provided you do it before development sets the image.

Modern darkroom workers who still process by hand have rediscovered this independently. The standard technique today is to "agitate" the developing tank by inversion, which works for roll film inside a sealed reel — but for sheet film and tray development, the bubble problem returns, and the 1910 solution still works. Some contemporary alt-process photographers (platinum, cyanotype, wet plate collodion) explicitly recommend a soft brush stroke across the surface during the first seconds of development, citing exactly the reason Barrows gave.

What was lost is not the chemistry — that's well documented — but the tactile confidence. Photography in 1910 was a craft you did with your hands, and your hands were tools, not contaminants. The shift to "never touch the emulsion" came later, with archival concerns about long-term storage of finished negatives, and the message bled backward into a blanket prohibition that would have astonished any working photographer of the Edwardian era.

It's a small reminder that "best practice" is often a frozen snapshot of one era's anxieties, mistaken for a law of physics.