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Instrumentation for Microtomy: Flotation Bath

A flotation bath or water bath is the intermediate step between cutting paraffin sections and placing them on slides. Simply sticking paraffin ribbons on slides will not work! A warm water bath allows tissue to relax and smooth out prior to being mounted on a glass slide. The warmth also makes the paraffin stick to the glass slides. Water baths are filled with distilled water, heated to a temperature 5-10° C below the melting point of paraffin, and the water bath is usually kept at 40-50° C. This is an optimal temperature range for various types of paraffins. Hard paraffin will require a higher water temperature to relax, while softer paraffins will benefit from a lower water temperature since they may disintegrate at higher temperatures.
Water bath facts:
  • Used to float paraffin ribbons, to stretch sections and remove wrinkles and folds before placing sections on slide.
  • 95% alcohol may be added to the water to lower surface tension and remove wrinkles.
  • Water temperature may need to be lowered for fatty tissue, such as breast or brain.
  • Sometimes adhesive is added to the water to aide in slide adhesion.
  • Water must be kept clean and changed at least daily.
  • Keep empty reservoir covered to prevent fibers and dust from settling and becoming a potential contaminant.
  • Reservoir must be cleaned daily and paraffin removed with gauze. It may also be wiped down with alcohol.
  • Water surface must be skimmed with a Kimwipe® or other laboratory-grade wipe to prevent contamination of debris between each ribbon.
  • A water bath that is too cold will not remove wrinkles in tissue sections.
  • A water bath that is too hot may melt the paraffin and change the tissue morphology.
  • The water bath may introduce artifacts to sections.