We have had similar problems with our DAB chromogen in the past resulting in a precipitate forming on the slides.  We later found out that the positive charged slides picked up the protein (gelatin) in the waterbath causing this precipitate to form.  Although the precipitate easily washed off, the tissue would often have a distinct smudge effect where the precipitate had formed.

We now change our waterbath after cutting the H&E's, wash thoroughly and replace with deionized water only before cutting any immuno slides.

Greg Good
Pathology Technical Director
Frye Regional Medical Center
Hickory, NC  28601
(828) 315-3680

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