Hello
We make up a 3.% aqueous solution of Potassium Dicromate
Here is a copy of our's

Prepare:
Potassium Dichromate...........30 gm
Distilled Water.............. 1000 ml

Wear a lab coat, eye protection and rubber gloves.
Potassium Dichromate is a nephrotoxic chemical that can be absorbed through the skin. In the even of contact, rinse contaminated skin with water immediately.
  Post-fix tissue for 2-4 hrs
  Rinse under running water for 4-6 hrs, place in container covered by gauze and secured with rubber band so that your cassett doesn't go down the drain.
This is for guinnea pig, mice, or rats
I usually don't leave rat brains in the K-Dicromate for the whole 4 hours do to the size of the tissue.

Also If the sections you cut are going to have Immuno"S stainning done on them I don't think you can use this procedure or profused the brains with 10%NBF.
This is being used for H&E staining.

With post-fixing the tissue the tissue seems to have more structure and is easier to cut.

If you need to , you are always welcome to call me at
410-436-1967
I hope this answeres your question
Have a great day
Sandi Miller HT
USAMRICD Research
Maryland