Red Litmus Paper

A qualitative indicator paper that shows whether a sample is alkaline, by turning from red to blue. It gives a yes or a no, not a value.

Why it is measured

The counterpart to blue litmus. Where blue finds acids, red finds bases: caustic carryover in a rinse, an alkaline cleaner still present on a surface, ammonia where there should be none.

Where it is used

• teaching laboratories
• caustic rinse verification
• alkaline cleaner checks
• quick base identification

What it answers

A qualitative paper does one thing and does it without ambiguity. There is no scale to interpolate and no lighting to argue about: the colour changes or it does not.

That makes it the right tool when the decision is binary — proceed or do not — and the wrong tool when anyone needs to know how far past the threshold the sample is. For a value, use an indicator paper with a scale or a meter.

Practical note

Keep red and blue papers in separate containers; once mixed they are indistinguishable after a sample has been run.

Supplied in 3 presentations covering different measuring ranges. The range is chosen by model: 8.0.