The Montblanc Compressor
Montblanc started experimenting with a new filling mechanism in 1923 - a pneumatic filler. Maybe the company wanted something more robust and distinct from the lever filler that was common with other brands. Pneumatic fillers were not entirely new technology. The very first version might have been a blow filler patented by Seth Crocker in 1901 (link to patent). The official document explains that "the sac is contained in an air-tight chamber, and then providing an aperture at the end of the barrel in its usual place when the pen is being used and a person blows into the end of the cap pressure will be created about the sack sufficient to collapse the same so that when the pressure is removed the sack may immediately expand and suck in the ink through the feed passage". As you can imagine, this was not very convenient. So, an iteration was made to the design in 1915 by Julius Abegg where instead of blowing into the hole to create pressure, a tube is pulled out and then while placing a finger at the bottom of the tube and pushing it into the barrel pressure is created that depresses the ink sac, and then releasing the finger breaks the vacuum and the sac expands and sucks up ink (link to patent). The idea behind this filler was to provide a larger sac size that would not be possible with existing filling mechanisms. This design was very close to the iteration patented in 1923 by Montblanc (link to patent). Chilton applied for a very similar patent granted in 1925 (link to patent).
S. Crocker 1901 patent
J. Abegg 1915 patent
Montblanc 1923 patent
Chilton 1925 patent
Here's how the Montblanc pneumatic system works:
1. Pull and slide out the bottom of the barrel with the brass sleeve, as seen in the video below.
2. Place your finger on the hole at the bottom of the cone/blind cap/turning knob.
3. Slide the brass sleeve back into the barrel with force. This creates high air pressure in the barrel and squeezes the sac. If the nib is submerged in ink at this time, you will see bubbles come out of the nib unit into the inkpot.
4. Release your finger from the hole to break the high pressure in the barrel. The air displaced in the sac forces ink back into it. Done!
A 1927 instruction manual "for use of the Montblanc-Automatic Filler"
Montblanc's pneumatic system was made for a short period between 1924 and 1929, with the Meisterstück and Masterpiece versions probably only sold between 1927-29. The pneumatic system is said to have been mostly exported to other countries, but in general, Montblanc didn't enjoy much success with it. Maybe the parts were too expensive, or maybe customers did not take too well to this mechanism in comparison to the safety fillers and lever fillers. Montblanc's pneumatic filler is popularly known as "Compressor". Pens with this imprint on the cap and body typically refer to the patent No. 400356. But, there are a few variations found.
The first set of variations are found on the imprints. There are four major versions: (i) "Compressor" imprints on the barrel and cap (ii) "Meisterstück" imprint on cap and "Montblanc" on barrel (iii) "Masterpiece" imprint on cap and "Montblanc" on barrel, and (iv) only "Montblanc" imprint on the cap and barrel
Montblanc "Compressor" belonging to Roberto C. Notice the matching "Compressor" imprints on barrel and cap.
MB dummy pen No. 4 with "Meisterstück" imprint on cap and "Montblanc" imprint on barrel.
1927 advertisement announcing, "The new Montblanc Masterpiece 4810 is now on the market". Notice the "Masterpiece" imprint on cap and "Montblanc" imprint on barrel.
1924 advertisement exclaiming, "At long last we can offer the new Montblanc self-filler. The lever on the side of the barrel, known from many brands, has been abondoned". Notice the plain "Montblanc" imprint on cap (and these versions also have a matching "Montblanc" imprint on barrel).
The second set of variations are found on the blind cap/end knob at the bottom of the sliding tube. There is (a) one-piece end knob with an open hole in the centre where one places their finger while filling the pen, and (b) two-piece end knob, where a small disc must be screwed off first to expose the hole where one places their finger. There was also a "pumpfiller" with an iteration of the pneumatic mechanism but that was a prototype that didn't go into commerical production (pictures can be found in Collectible Stars I).
No. 4 Montblanc pneumatic filler from my collection. Notice the one-part end-knob.
A disassembled black No. 35 Masterpiece (top), and No. 35 red (bottom). Notice the one-part end-knob.
Montblanc "Compressor" from the collection of Roberto C. Notice the two-part end-knob.
Montblanc "Compressor" from the collection of Eric B. with two-part end-knob, and barrel and cap imprints.
Which version of the pen came first? We don't know. Why were two versions of the end-knob made? One might speculate that the two-piece nob came first and might have been found too cumbersome to use and thus replaced by the one-piece end knob. However, there is no evidence for this view. Why didn't all the pens have the "Compressor" imprints? We don't know. But, some experts believe that the "Compressor" model signifies the two-piece end-knob variant, while the one-piece end-knob variants are simply pneumatic fillers. Also, to confuse us further, examples of pens with a mix of imprints and end-knob variations often present themselves :) Maybe, repairmen replaced parts with substitutes from other models? Or, maybe Montblanc started mixing and matching parts towards the end of the model's production life in order to utilize all extra stock of parts? No one knows! The pens are rare and beautiful either way if you ask me!
No. 6 Compressor belonging to Joudenali. Notice it has both - "Compressor" imprint on cap, "Montblanc" imprint on the body, and the one-piece end-knob.
No 2 Rouge et Noir Compressor. Notice the "Montblanc Compressor" imprint on cap, but "Rouge et Noir" imprint on body.
Source: Fountain Pens of the World; A. Lambrou.
No. 4 Compressor belonging to Azad B. Notice it has the "Meiesterstück" cap but "Compressor" body imprint. And it has a curious saw mark on the barrel and metal sleeve (to support function of the filler?).
Compressors came in black, coral red, and red ripple colours, in sizes No. 1, 2, 4, 5, 6, and even a rare size 8 has been reported by an expert. They also came in No. 25, 35, and 45. These pens are large in general and have a substantial heft to them because of the brass sleeve which is part of the filling mechanism. Pneumatic fillers are amongst the rarest Montblanc models, coveted by collectors today!
For bibliography, see Resources page -->link