The blue litmus will turn red or pink when it comes into contact with an acidic solution below pH 4.5. Between 4.5 and 8.3 the paper will be purple. Above 8.3 it will stay blue. Supplied in plastic vial, about 100 paper strips/vial.

Litmus paper is NOT used to determine the pH level of a solution. If you need to find out the pH level, the correct test paper to use is the pH paper.

Blue Litmus test paper is a foolproof pH test to determine if something is acidic. The Blue Litmus test paper does not come with a color chart as it cannot provide you with a defined pH value. The test strip will turn red if dipped into an acidic solution (pH <7). It will remain unchanged in an alkaline solution. Although there is no color chart, the strip will turn various shades of red, getting darker the more acidic the solution. We have tested the blue litmus with multiple pH buffers. The blue paper is blue at pH 8. At pH 7, the sample is maybe just a little red. The real change to red seems to start with pH 6.5 and lower.