In 1827, during Niépce’s stay in Paris, Daguerre shows him how he plans to capture the images taken by a camera obscura. Once the image is projected inside the camera, the luminal energy is absorbed by a layer of phosphorescent powder and reflected as a light emission. Unfortunately, the resulting phosphorescent image inside of the camera obscura cannot be permanently fixed but fades progressively.
In December 1829, Daguerre visits Saint Loup de Varennes to sign the agreement that links his work to Niépce’s. He brings along some yellow phosphorescent powder.

The National Heritage Days 2006 were dedicated to Daguerre’s four stays in Niépce’s House Le Gras in Saint Loup de Varennes:

1) In December 1829, Daguerre and Niépce sign their collaborative agreement; Daguerre receives Niépce’s “Notice sur l’Héliographie” (i.e. his “Note on Heliography”).
2) In June 1830, Daguerre for the first time brings along the residue of distilled lavender essence
3) In summer 1832, the two partners invent the physautotype
4) In November 1832, the two partners try to improve the process of the physautotype

On the National Heritage Days 2006, the visitors at Niépce’s House could assist at the development of images on phosphorescent powder that were exposed inside a camera obscura during their stay. On leaving the house, they could admire the phosphorescent images recalling those taken by Niépce and Daguerre in December 1829, at the very same place.

For the details on the production of phosphorescent images, see “Niépce, l’invention de la photographie” (i.e. “Niépce, the invention of photography”).