What technique involves wax impregnation under negative atmospheric pressure?

The technique that involves wax impregnation under negative atmospheric pressure is vacuum embedding. This method is used to ensure thorough infiltration of the tissue samples with embedding medium, typically paraffin wax, by creating a vacuum that draws the wax into the tissue. The negative pressure helps to remove air bubbles and promotes better penetration of the embedding material, leading to well-preserved samples that are easier to section and analyze.

In contrast, the other mentioned techniques either do not involve vacuum or utilize different embedding processes. Double embedding, for example, often involves two different embedding media but does not rely on negative atmospheric pressure for wax infiltration. Standard embedding typically refers to using standard methods of embedding without the application of vacuum, while heat embedding uses heat to facilitate the melting of the embedding medium but does not employ a vacuum to assist in the process. Therefore, vacuum embedding stands out as the most relevant technique for wax impregnation under negative atmospheric pressure.