Increase the time and/or temperature. I bake mine at 85 Celsius for 20 minutes on non charged slides. Section thickness is also a factor as well as the pH of your blueing reagent. -- Tony Auge HTL (ASCP) QIHC Histology Supervisor - Chandler Pathology Services Cell: (651) 373-4768 Email: tony.auge <@t> gmail.com