The methods that can be used to develop indented writing are oblique lighting, ESDA, UV. If a document is written while resting atop other papers, impressions of the writing will be transferred to the underlying sheets. If heavy pen pressure has been used, indentations are often seen when the document is illuminated with side-lighting. A more sensitive technique is required to view indented impressions produced by normal or light pen pressure. (ESDA) is a special instrument capable of restoring handwritten impressions in paper that are completely invisible to the naked eye.