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“Adamantine” was Seth Thomas’ trademarked name for a celluloid finish over wood. Besides the mahogany color shown here, it was made in black, white, green, brown, tan and other colors. These cases are durable, and can usually be polished to look very nice. Sometimes the colors fade with age. Adamantine clocks were made from about the 1880s to the 1920s.

This beautiful mahogany Adamantine clock came into my shop recently with a broken time mainspring. Nothing too exciting about that, but I think this clock is so nice looking that I decided to show it here. I had previously repaired it 11 years ago, overhauling the movement and polishing the case and bezel.

I replaced the broken time mainspring with a Merritt’s P-1956 3/4 by .0165 by 96 inches (the original spring was 0.0172 inch thick). The pendulum takes a superb motion (almost too good) and so an even thinner mainspring would work. During my previous overhaul, I replaced the way too strong strike mainspring (an incorrect replacement) with a spring about 0.016 inch thick.

Repair job 4981.

I just repaired this Seth Thomas mantel clock in a mahogany color Adamantine case. It has a No. 89 movement with a solid back plate. The case is 16 1/4 inches wide (including feet) and 11 inches tall. The bottom of the case has date code 81B (February 1918).

The escape wheel had two teeth that were too short due to damage by a previous repairer. The slide show below shows that the damaged teeth were removed, a brass plug inserted, and then 2 teeth filed to shape.

Both mainsprings were original Seth Thomas springs, one .0177 inch thick and the other .0165 inch thick. I don’t know for sure which one was originally on which side (time or strike). The .0177 inch thick spring was too strong. The thinner spring did not unwind smoothly. I replaced both with Merritt’s P-1956 springs 3/4 inch wide x 0.0165 inch thick x 96 inches long.

One thing strange about the case is that one end is mahogany Adamantine, but the other end is black! (see slide show below). It appears to have been made this way.

Repair job 4830

I repaired this Seth Thomas Adamantine clock last week. The movement is No. 89C, a popular movement for mantel clocks, using a semi-deadbeat escapement. This one needed a lot of work, including making a new dial (it had a terrible replacement dial), making a new front strike mainwheel bushing, and replacing both click rivets and clicksprings (the clicksprings were the unreliable flat steel type, one of which was broken). I routinely replace these with round spring wire springs. See the slideshow below for photos of some of the repair steps. Here are some movies of this clock in operation:

The time mainspring is 0.016 inch thick (thinner than average) yet the escapement takes a great motion!

Here is a slide show of some of the repair steps:

Job 4767.

I did not repair this clock, just oiled the bearings and regulated it. It has the model name “Sparta” and a date code on the bottom.

The date code is 1901

This movement with the escapement at the back was used until about 1901 in Adamantine mantel clocks. It was superceded by the no. 89 movement. Note: the brass j-shaped turnback lever is not in the correct position because the previous repairer assembled it incorrectly. The long part should be on the left (time train side) and should have free movement toward the time train. See this post for how it should be.

As received: the time mainspring was 3/4 inch wide by 0.0175 inch thick, and the strike mainspring was 0.0165 inch thick. There was very bad T4F pivot hole wear. The strike train had virtually no wear.

Showing front time pivot holes 3, 4, and 5 before bushing. Note excessive wear on #4

After the overhaul, (I did no bushings on the strike side), the pendulum motion was excessive, and the striking sounded sluggish. I swapped the time and strike mainsprings, and then the pendulum motion was excellent (could still have been less) and the strike sounded fine. Here are the final values of the mainspring sizes (remember that these are ORIGINAL OLD mainsprings, if they were being replaced, thinner spring should be used):

Time Spring: Original old 3/4 x 0.0165 inch

Strike Spring: Original old 3/4 x 0.0175 inch

The bottom of the clock showing date code “6091L” which means December 1906.

My job no. 4487