Do you think an evap line can have colour that gets darker over time?

Question

Answer

The answer is sometimes, but it's highly dependent on the brand, test style, dye color and time the evap shows.

Blue dye tests absolutely can give colored evaps within the time limit. Usually, the line is thin or very, very faint. It's a flaw in the dye that reacts with the acids in the urine and/or the nature of the blue dye crossing a test strip made of gold (which all pregnancy tests have) reflecting enough light to create the illusion of a super faint line.

With all pregnancy tests, as the test dries (and especially if you've moved it around a lot) excess pee and dye in the wick will creep up the test area as it dries. The positive area also becomes more visible because it's stamped onto the strip, causing an indent or depression. Sometimes the dye pools and settles in these, making it look positive. This causes evaps and it's why you don't read the test after 10 minutes.

Dip strips and cassette style tests tend to be cheaply made, so their antibody strips (where lines go) tend to be more visible when wet. Those lines will appear grey, but grey on a pink background as the dye runs up the test can look pinkish. And grey can be hard to distinguish from very, very light pink.

The above can happen with more expensive name brands, too. FRER can have some wicked indents. CBE's test line reflects a lot of light.

My rule of thumb is a true positive is one that you don't have work to see. It's apparent in the time limit. And when I test the next day, it's as dark or darker... Basically, when in doubt, I throw it out.

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Do you think an evap line can have colour that gets darker over time?

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