One question I have heard in relation to custom horn makers is this; are they just assembling parts? What makes them better than just buying a factory horn?
Horn assembler, or horn maker?
Typically, brass instruments are made in a factory setting. The largest makers may have hundreds of employees, most of whom specialize in certain steps in the production process. And being a large shop, while they would buy the tube from a tube maker, those big makers typically do everything else; they make the valve sections, make the bells, make all the parts and bring it all to completion.
Some horn makers are smaller, but are still a shop with multiple employees. Depending on their skillsets and how far they want to take it, those makers could make it all, but may choose to buy bells and/or valve sections from shops that specialize in making bells and valve sections. Not to mention other parts such as the small, second valve tubes and braces may be purchased.
A side point worth mentioning as well, smaller makers typically don’t make nickel silver horns. Nickel silver is more difficult to work with and to obtain in smaller quantities.
Then we get to a one-man shop like Geyer. He did not do it all. In short:
It was a custom horn, but some key parts were purchased
Go back to the quotes in part III (here), you get a good visual idea of the Geyer shop. He did have a lathe for making some parts, and a buffing machine to bring instruments up to their final finish. He had some space to spread out and work! But he did not have a giant lathe setup to make bells, or all the equipment needed to build and braze together a valve section, for example.
In part I of this series (here) I mentioned that according to Milan Yancich, Geyer first made his new design in 1923, and that a Geyer style Geyer horn with a serial number of 223 exists – which should date to February of 1923. This horn was previously in the collection of Vince Kavalovski, and is currently owned by John Wunderlin. It will serve as a good model to look at in relation to how these were built, with the final photo showing the horn after restoration by Ron Pinc.
UPDATE: Please see this article for more on this horn, which actually likely dates to the late 1930s or early 1940s — Geyer did not always follow his serial number system.
As indicated already, there were two very key parts Geyer simply had to purchase: the bell and the valve section. While to a point bells are bells, as this horn was a new design, he would have had to share some information about what he was doing with his valve maker in Germany to have this exact valve section produced. While only speculation on my part, this could be another source of how Knopf learned of the design.
What is especially interesting about horn 223 is what we would think of as a Knopf style body. Today we conventionally think of Geyer horns having a straight profile across the four valves, but this one has the curved crook out of the first valve. In any case, though, Geyer did not make that valve section himself, that came from a third-party maker. More on the topic of Geyer and Knopf and the lack of a patent on the design may be found in part 2 of this series.
And note the layout of the tubing on the back: this is the iconic layout that defines the Geyer/Knopf wrap.
Some parts were made in his shop
It should be stated clearly that Geyer did make many key parts of his horns. He certainly was set up to make all the tapered tubing on the horn before the bell tail. That would in particular be the critical lead pipe and first branch tapers. Either of those two parts, not made very well, will leave a horn playing not very well.
In addition, you have bracing that is not just there for bling! On the horn it takes makers years to figure out optimal bracing placement, and it makes a big difference. Over time, if you look at older and newer instruments by custom makers, you will see some evolution of this design element, and others.
Speaking further about braces, while he could have taken the time to make all the braces, he may not have bothered to do the small ones, as it is very possible to buy these parts. On this horn, all the nickel silver parts were likely purchased rather than made.
Turning to the bends in the tubing, all the larger bends he of course did, and I believe he was capable of making the 1st and 3rd F horn valve slides as well (although perhaps they were purchased). But the small crooks like on the 2nd valve slide, those were certainly purchased, as were the bows of all the other tuning slides.
You will notice that horn #223 is essentially all brass. As mentioned earlier, brass would have been easier for him to obtain in smaller quantities, and building in all brass became over time part of what makes the look and feel of a traditional Geyer-style horn. Dare I say even, the magic of the horn?
How does #223 play?
Returning to the horn seen in the photos in this article, current owner of Geyer 223 John Wunderlin reports that the horn has a very narrow bell throat. Also, quoting him, “The horn has terrific intonation but it tends on the flat side.” Which I found very interesting, as my Geyer single F also is built a bit flat to my needs.
My single F was a horn I worked on during my sabbatical project, and is described more here. It came to me minus the bell, and with an unusable Geyer lead pipe (the previous owner had used the bell to restore another Geyer horn). I saved as much of the remaining Geyer as I could, including the long pieces of bent tubing and the first branch. I always like pondering these parts, ones that were clearly made by his hands.
There was some variability of exactly how he made instruments
Geyer made horns for a long time. The design evolved due to improvements and also adjusting things in relation to the purchased parts available to him. Keep in mind also, each horn was a custom order, made with a specific individual purchaser in mind. He did not sell a one-size-fits-all horn; every horn was made to suit a specific buyer.
A really clean design
Backing up to the topic of what was unique about the 1923 Geyer double horn design, it is very open around the valve section. In recent work on my Kruspe and my Patterson Geyer I had the three valve levers off both horns (putting dimes on one and taking dimes off the other). The Kruspe, with that tube between the valve section and the bell tail, it was quite a chore to fish things back into place. On the Geyer, it literally was a breeze. He must have really appreciated this over building the Schmidt style horns he built before 1923. Not to mention the thumb valve position and action really is much better on the Geyer than on my Kruspe (or on a Schmidt style horn).
The birth of the custom horn market
Finally, I’d just mention that within our USA context, Geyer created a market that survives today, the custom horn made by the lone maker or very small shop. I could name several easily, and it is to Geyer that we owe the creation of this market.
Geyer recognized also that the horn was only part of the equation, you needed a good mouthpiece to go with it! When the series returns, we will look more at Geyer the mouthpiece maker.
Keeping a journal and talking openly to other people about your mental state can be very helpful. There is nothing shameful or wrong with having anxiety issues, asking for help, or taking anxiety medications.
Introducing Carl Geyer
This example is from I would guess around WWI. (UPDATE: Unfortunately, I did not make note of or take a photo of the engraving. 
Postwar comparison
This series is probably not over but will be on hiatus for a little while! But be watching for a Geyer Dreaming series soon.