'Puffed' heart center medals, usually with a Marion monogram, are from the late 1800s through the first part of the 1900s. They were especially popular in Germany and Belgium.
Rosaries made through the mid-1860s commonly had simple heart-shaped center medals depicting the Sacred Heart, Mary, or a stylized M. Toward the end of the 1800s and into the early 1900s, it's common to find center medals facing "upside down".
Miraculous Medal Centers
Miraculous Medals were first struck in 1830, but the medals weren't used for rosary centers until late in the 1800s.
Scapular Medals Centers
Scapular center medals (Sacred Heart of Jesus on one side and Our Lady of Mt Carmel on the other) were introduced in 1910, by papal decree. They quickly became popular, both as medals and as rosary centers.
Separately Nailed Feet
Showing the feet side by side, with a nail in each, is common in crucifixes before approx 1830. More recent crucifixes occasionally show the feet this way, but overlapped with one nail is the usual configuration.
Through the mid 1860s, rosaries frequently had simple crosses without a corpus.
Skull & Crossbones
The skull and crossbones often shown at the bottom of old crucifix are intended to show triumph over death. They also commemorate the site of the crucifixion on Golgotha, the "place of skulls". Sometimes called a Momento Mori (Remember That You Must Die), but that term really applies to skull beads and centers.
1830 to 1900+ Composite Crucifixes
In the Victorian era (1837-1901), composite crucifixes were common. These crucifixes might be a combination of a wood cross wrapped with aluminum or brass, and a metal corpus. Metal crosses with a thin layer of wood or mother of pearl inlay were also popular and featured a metal corpus. Celluloid was another popular layering material that sometimes took on the appearance of ivory, tortoise shell, or mother of pearl.
1830 to 1910+ Stamped Metal
Stamped Metal crucifixes were common during the Victorian era, including those which featured a crucified Christ on one side and Mary on the reverse.
1864 Stanhope Viewers
Tiny peephole viewers followed the invention of the photograph in the mid 1800's. They were especially popular from 1870 - 1920s, and were still made at the end of the 20th century.
The most popular style of Stanhope was made of carved bone and featured tiny pictures of Pilgrimage sites. These were produced from 1864 through the early 1900s.
Approved and promoted by Pontifical Rescript onJune 1, 1905. Ecclesiastical Sanction, January 15, 1907 .
1905 Pardon Crucifix
1940 to 1970 'I am a Catholic'
In the mid 20th century many rosary crucifixes had the message, "I am a Catholic. In case of emergency please call a Priest." or "I am a Catholic. Please call a Priest." inscribed on the back. Military rosaries tend to have the second expression whereas non-military rosaries tend to have the first. Though you can still find some crucifixes with this language today, it was mostly discontinued by the 1970s.
1964+ Scorzelli Crucifix
Lello Scorzelli was born in Naples in 1921 and died in Rome at the age of 68. His best known work is the staff with the rugged crucifix on top that was created for Pope Paul in the mid-1960s. The piece has become closely identified with the pontificate of Pope John Paul II, and was the model for the crucifix on the rosaries Pope Benedict gave to his guests.