Stacy, The German handgathered marbles IMO date from the 1850-70s for the ground pontil types to the 30s when Gob feeders started to be used. Most handgathered do not really have a pontil but a shear mark that shows as certain shapes depending on type of shear method of rounding and temp of glass when sheared. Personally I believe German marble machines and their use followed about the same timelines as American manufacturers. I know of no real good books on this subject. I have gotten a lot of information from adds in toy catalogs pamphlets ect., original packaging and from what other marbles were often in the groups with the handgathered marbles. There is one Block book titled Collecting Early Machine Made Marbles that deals with a lot of the Handgathered marbles. It has many good pictures. I also have some of the "Canadian" types and American handgathered slags in different containers.