Why do preparations fall off slides? Why wash slides in acid before use?
Slide ‘Washing’: We clean new microscope slides by soaking in chromic acid for 3 hours (to one month – two batches are always soaking). For years, we called this washing, but new slides cannot be seriously greasy/dirty. But we knew that omitting the step often lead to selective loss of metaphase spreads and poor in situ results. Now we think the soaking neutralizes the sodium hydroxide used in glass manufacture: without neutralizing, oil in the preparations will turn to soap, and the pH will change during hybridization (SSC is a poor buffer). The result also explains why some slide makes/batches do not need soaking – they have less residual NaOH.
