We recently published a chapter on serial section methods in Methods in Cell Biology, Vol. 48, Academic Press. H. Epstein and D. Shakes, Eds. David H. Hall 7. It makes us better here when it comes to doing our own in-house work and of course, it makes us better in giving expert customer technical service when one of our customers has difficulties.
Sections are too thick, causing a heat buildup.
If yes, then that could be your problem. Only one or possibly two of these products have the right characteristics for this particular application. We know exact what is the correct product when we purchase it to fill our bottles. The TEM grids you are using could be a problem also, since we know that from some source, the slotted grids are not as flat as they ought to be, causing the section to be position independent in terms of what is focus. To my way of viewing things, this variation should not be enough to cause a focussing problem, but others seem to believe other wise.