Trismigistus, do carry on. This detective work must be done as devoid of personality/ego/belief as possible to get closer to the most likely time before print.
I went to that site and looked for evidence of age. By evidence I mean a dated nameplate on one of the machines, a component of the machines that could lead to an invented process or a paper trail.
As you discovered so did I.
If there is dating evidence in the museum its not available anywhere in digital form.
The component and construction materials appeared to be a dead end. Wood, malleable iron, possibly bronze are the materials used to produce the machines. They are likely to have been repaired if they are anywhere near as old as claimed and if the source of age is a paper trail then there will be paper detailing repairs. Once again not digitised.
In the repair it is feasible steel components replaced malleable iron and possibly bronze. Speculation obviously.
Looking at the machines, ignoring the names most pointedly, I could not see where to go next so began looking for the 'Chinese connection'.
Turns out that porcelain was apparently used to produce the Chinese type. Porcelain is a high fired conglomerate of China clay with additions so its safe to suggest the Chinese type cutters either cut a mould for each character and pushed the China clay mixture into it to get the characterr impression in reverse or cut the clay whilst still wet.
Either way when fired the resultant porcelain would be hard enough to take ink and the pressure of a roller and paper to create a printed page. Readable and likely crisp.
The problem porcelain has it is brittle and given the nature of the Chinese character alphabets intricacy I would suggest failure was common place.
As an aside here is an article from Korea which reveals how little if anything the official historians and academics actually know.
Report finds oldest movable type to be fake
I came back to the claim of the oldest presses and just sat looking at them. It dawned that I should be looking for the fundamental that the machines are built on.
I realised its the type itself.
The rest of the machine is a simple press. Presses are used for all sorts of things and they seem to have been in existence for along time. The basis of a press is a means of applying a pushing pressure onto something to get a result that could not be achieved without the pressure.
At its most basic its a lever attached to a spindle, secured in a strong frame, which when pulled forces the spindle and whatever its connected to down onto something.
A cam or inclined plane at the base allows for fast controllable effective repetive use.
One such use would be a brick press or a ceramic plate press, another could be a juice press although instead of a lever there would be a wheel and there would be a screw thread cut into the spindle and its stock to keep increasing the pressure.
Paper is produced using a press to achieve a usable, durable surface. Paper production does not require pressure from a press but the press does speed the process up and standardises the paper thickness.
The Chinese type was not movable apparently. It is claimed the Chinese typesetter carved an entire page or two page spread at a time and printed from it until it broke then they had no choice but to carve a new version of the same page.
This led to a Chinese inventor creating movable type where each character is an indfividual type and they are compiled together in trays to create the page to be printed.
Movable Type — the very first printer and a brief look at its history
So the movable type is claimed to have been invented thousands of miles away from any other culture in one single culture for its own use.
This led me to look at what is the gain from printing over hand written or oral recitation.
The most obvious gain is repetition of the same text. It is carved/compiled once and any number can be printed off as long as there is sufficient ink, paper and crispness in the printed page.
This leads to a speed if dissemination of these printed pages that neither oral or hand writing could match.
It also makes indoctrination by the written word more widespread.
It increases the number of people who are taught to read.
It allows whoever is creating the source document to change it with ease.
It allows an easy faking of texts.
It allows eassy manipulation of attribution and dating.
It locks new words into the written and then spoken language via dictionaries than hand writing does.
It also allows the degradation of words.
Finally it allows definitions to be quickly and easily altered.
I'm sure it does other things not least of which is fixing a history in place.
This got me to thinking about what the type is made of as it alone is what makes the press a printing press.
According to this site its a specific alloy that has been around for 550 years. It is alloy of lead, tin and antimony.
Movable type - Wikipedia
Lead, tin and antimony is also known as solder. I used this formulation to solder copper, brass, bonze pipes in my shipyard days. I used a lead, tin solder to solder lead as it is lower melting and can be wiped with moleskin.
The addition of antimony and a change in the ratio of the lead and tin makes the solder harder.
Both can be flattened and knocked very thin with a steel hammer on an anvil but that is the only similarity they have in terms of hardness.
Ignoring the attribution given to Gutenberg who apparently was the man who brought a press to Europe, though where from I have yet to look for, the fundamental remains the metal alloy for the type.
How was it discovered, by what trade, how was it established that this specific alloy performed better than the alternatives?
Secondary to that is what trade was the printing press adopted from?
Which people or tradesmen are candidates for developing the alloy, developing the mechanism of the press to make the most of the alloy and who is most likely to have the know how or desire to bring he various disciplines together to develop the new machine to the point it is reliable and effective.
Its seems the press predates the use of a press for printing.
It also seems the solder of lead, tin and antimony and its use predates the invention of metal movable type.
With that alloy it is easier to carve a master mould then cast any number of identical copies from it.
I say this as I was taught to easily melt soft solder from old joints in a small steel ladle and pour it out into channels in sand or angle iron to get useable flat lengths. I did the same for recovered hard solder though I used angle iron not sand to cast it.
From the Belghian museum page the claim is the type for the presses was carved in France by the French type carvers. Carving such things by hand and getting a consistency across carvers must have been a nightmare whereas if the carver simply produced a master mould the type casters would be trained to produce identical copies of the master.
The latter makes much more sense on every level but then again truth be told I am here looking back so could be off beam.
Other sites I read through.
World’s First Metal Type | Explore DPRK
Movable Type – History of the Book