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 before being mounted on a glass slide. The warmth also makes the paraffin stick to the glass slides. Water baths are filled with distilled water and heated to a temperature of 5–10°C below the melting point of paraffin, usually 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, stretch sections, and remove wrinkles and folds before placing sections on the 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) and brain tissue to avoid section explosion.
- Sometimes, the adhesive is added to the water to aid in the adhesion of the tissue section to the slide.
- Water must be kept clean. It should be completely changed at least daily or more frequently depending on the number and types of blocks sectioned.
- Keep the empty reservoir covered to prevent fibers and dust from settling and becoming a potential contaminant.
- Reservoir must be cleaned daily, and paraffin must be removed with gauze. It may also be wiped down with alcohol.
- The water surface must be skimmed with a Kimwipe® or other laboratory-grade wipe to prevent debris contamination 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.
