Those new to the wooden flute often have to navigate some confusing territory, as the design of the instruments is generally less standardized between makers than that of silver flutes or violins. This is particularly true when it comes to the specifications of the headjoint, and there are many choices and differing opinions as to what is best. Some players prefer a headjoint as much like those of the original 19th century Nicholson flutes as possible, which were fully-lined with brass tubing and featured a thinner wood head tube than the earlier London-made flutes. This thinner tube dimension means that the embouchure “chimney”—the measurement from the inside to the outside of the flute—is not as tall as on earlier flutes. While this makes for an amazing tone in the hands of a skilled player (part of the revolution Charles Nicholson helped to bring about), these flutes are not always as easy to play for someone with less experience, and a taller chimney seems to provide a consistent sound more easily. Also, the mouth-hole size (embouchure) changed during Nicholson’s time. In the 1820's they were usually smaller, measuring about 9×11mm but by the 1850's had grown to a size of approximately 10×12mm, which is closer to both the Boehm flute and the wooden flutes of today. While a millimeter may not sound like much change, it has a significant effect on the way it feels to play the flute.
Even more confusing is the discussion of fully-lined versus half-lined headjoints. All of the flutes crafted by English flute makers during the period from 1820-1880 (with the exception of Monzani) featured fully-lined heads, as part of the new flute sound that was becoming popular at this time was a more “metallic” or powerful projection. Everyone who heard Charles Nicholson play was astonished by the sound, and most players joined this new school—in addition to playing very loudly, Nicholson was able to produce a wide palette of tones and play expressively at quieter volume. In France meanwhile, the fully-lined headjoint did not become popular, and all headjoints were half-lined, with a two-piece metal tuning slide that did not extend up to the embouchure and left the upper part of the headjoint unlined. (Johann Joachim Quantz had said in his 1750 treatise on the flute that a lined head had been tried, but “rendered the sound harsh and disagreeable.”) French flutes also featured the earlier smaller fingerholes and consequently played with a lighter, less forceful tone. As a result of these variations in design, there were two different schools of playing during this period, and they were grounded in different aesthetics (American flutes, principally made in New York City, fell somewhere between the French and English designs).
Currently, we make both half-lined and fully-lined headjoints and find that the differences between them are slight and that often it is impossible to tell the difference, practically speaking. Patrick sometimes prefers a fully-lined head for session playing, as he feels he gets more projection with less effort, but Aaron has in the past preferred his half-lined head and finds it is as loud or louder with less effort and with a lighter weight. That said, Aaron did a double-blind test with multiple tries of both and only guessed correctly 5/10 times. That being no better than the odds of a coin toss, it just goes to show that even for a seasoned player, the difference is minimal at best. Ultimately, the difference between the two flutes is quite small and difficult to quantify.
Also confusing is the assertion made by some that a lined head will always crack, or crack more often as the wood will continue to shrink. In our experience this is not the case—a piece of blackwood is not like a black hole, continuing to shrink forever, but will only do so while losing moisture, and once fully-dried, becomes quite stable. It is true that gluing a metal tube into a cylinder of wood is a cockamamie design from an engineering standpoint (as the wood does expand and contract somewhat with changes in humidity, whereas the metal does not) but with reasonable care, problems can be minimized. You have to be careful traveling from wet to dry climates or vice versa (say, from Ireland to your home in the desert near Phoenix) but an all-wood flute with no metal tubing can also crack under these conditions. Please see our “Care and Feeding” post for more information about humidity and its effect on wooden flutes. The early advertisements from the 19th century for the then-new lined heads maintained they wouldn't crack, as the lining made it more difficult for moisture to be absorbed into the wood of the headjoint, so it’s easy to see why there is so much confusion on this point.
Ultimately, choosing a headjoint comes down to the inclination of the player, and your best bet is to try as many as possible and decide whether you have a preference (but in this case, the variation is so slight that we feel obliged to say, "don't overthink it!")