Nuclear bubbling occurs when the proteins in the nucleus coagulate. This artifact is often a result of poorly fixed samples that have encountered a high level of heat. After sectioning, wet slides are often placed in an oven to dry. High temperatures (eg, 70°C) can cause the water under the section to rapidly evaporate through the tissue. The evaporation can cause the proteins to coagulate, giving the soap bubble artifact. The best way to avoid bubbling in this case is to either lower the oven temperature or allow the slides to somewhat airdry prior to placing them in the oven.