Congo Paper MN 816 N

A qualitative indicator paper that shows strong acidity, changing between pH 5.0 and 3.0. It gives a yes or a no, not a value.

Why it is measured

Congo red transitions in the strongly acid region, where ordinary indicator papers have already run out of scale. It is the paper for telling a mildly acid sample from a genuinely aggressive one.

Where it is used

• strong acid processes
• pickling and etching baths
• acid rinse verification
• industrial laboratories

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

Congo red also responds to some metal ions; in a plating bath treat a colour change as a reason to confirm, not as a pH result.

Supplied in 2 presentations covering different measuring ranges.