The water bath is an essential step in the histology process, which allows the paraffin ribbon to smooth out and stick to the glass slide when placed. The temperature of your water bath depends on the type of tissue that you are processing. A good rule of thumb is keeping your water bath 5-10 degrees Celsius below the melting point of your paraffin. This is generally in the range between 42-50 degrees Celsius. The harder your paraffin, the higher the temperature of the water bath can go. Softer paraffin in too hot of a water bath may disintegrate.
Another factor to consider when setting the temperature of the water bath, is the type of tissue. Fatty tissues, like breast or brain, prefer a slightly lower temperature water bath while muscular or vascular tissue like it hotter. If your water bath is too cold, you won’t remove the wrinkles from the tissue, however if the water bath is too hot, you run the risk of the tissue tearing up or exploding.
In order to reduce contamination of the water bath, use a thermometer for checking water temperature. Your fingers should not be entering the water bath. Forceps can be used to place the tissue into the bath.
If you are unsure about the melting point of the paraffin you are using, check the SDS (safety data sheet).