Anyone familiar with ambrotype photography that was suppose to be used during mid 1800's? Is there a collection or database of photos there?

That time was the childhood of my great grandfather Calixto Madera (1853? - 1923). and my great great grandparents Patricio Madera (1792 - ?)/Maria Dimas De La Paz (1819 - 1885)

That would be great to find old photographs of them.