Measuring Graduates

Overview

Every dilution in the darkroom is a ratio, and every ratio depends on measuring both parts accurately. A 1:1 dilution made with a 500 ml beaker and a 600 ml beaker that is really 580 ml will not be 1:1 — and you will spend months wondering why your times do not match the data sheet.

You need at least three sizes. A small graduate of 25–50 ml for concentrate, a mid-size of 200–600 ml for stock dilution, and a large 1000–2000 ml jug for mixing working solutions and water baths. A syringe of 10 ml is more accurate than any graduate for the small volumes one-shot dilution demands.

Read the meniscus at eye level, on a flat surface. A graduate read from above or below will be out by several percent, which is more than the tolerance of the chemistry.

What it does well

• Makes dilutions actually repeatable
• Polypropylene survives dropping on a darkroom floor
• A 10 ml syringe beats any graduate for small volumes
• Colour-coding one graduate per chemistry prevents cross-contamination
• Cheap enough to own a full set

Safety notes

Working notes

• Measure the concentrate first, then add water to the final volume — not the other way round.
• For one-shot dilution use a syringe; six millilitres is too little to read accurately in a beaker.
• Keep one graduate per chemistry and mark it with tape.
• Read the meniscus at eye level. Looking down at a graduate is the most common source of error in a darkroom.

Compatible with