Guild rituals

The next step here is to establish what the guild rituals are. For that, I needed the formula for Gutenberg's ink, especially to determine the metal content. Here is what I found first:

The ink used by Gutenberg was also a new development. It was not really ink at all, more like a varnish or oil paint. Unlike writing-ink it is oil-based, not based on water. Water-based ink would simply run off the metal types whereas the thick, viscous oil-based varnish sticks to them.

The black colouring of the ink is carbon - perhaps lamp black. Under the microscope, small reflective grains are visible distributed randomly throughout the ink. They are likely to be graphite - highly ordered carbon. These particles may be intended to improve the quality of the ink or be a by-product of the processing of the carbon to make the ink. More information on this analysis.

Gutenberg's printer's ink is distinctive in having a glittering surface. This is because of its high level of metal content, in particular copper, lead and titanium. It also contains sulphur.

The printer's ink was made up in batches, and was of course hand-made. Cyclotron analysis has enabled us to distinguish between batches and that has enabled us to understand much more about how the work was organised in Gutenberg's workshop.
The British Library

This is significantly different from the Iron Gall Ink that Jason mentioned in a previous comment that was used by scribes. It was made from iron salts and tannin from vegetable sources.

The ink was generally prepared by adding some ferrous sulfate (FeSO4) to a solution of gallotannic acid, but any iron ion donor can be used. The tannic acid was usually extracted from oak galls (also known as "oak apples" or more correctly Oak marble galls), or galls of other trees; hence the name. Fermentation or hydrolysis of the extract releases gallic acid, which yields a darker black ink. The fermented extract is combined with the ferrous sulfate and a binder such as gum arabic.

After filtering, the resulting pale-gray solution was used to write on paper or vellum. A well-prepared ink would gradually darken to an intense purplish black. The resulting marks would adhere firmly to the vellum or parchment, and (unlike india ink or other formulas) could not be erased by rubbing or washing — only by actually scraping off a thin layer of the writing surface.

That it can be completely removed was sufficient to allow this ink, or a galloferric ink with added carbon black, (lamp black) to be used in making Torah scrolls - if a letter is ever found cracked, common with a vellum document rolled and rerolled daily, it must be removed in its entirety before it is redrawn for the scroll to remain ritually pure. This has led to many a "red" Torah where over the years the ink reacted with oxygen and changed to a reddish color, which is not kosher for a Sefer Torah (the ink must be black).
Wikipedia

I'm thinking that because of Gutenberg's association with the goldsmith's guild, the secret craftsmen's association that holds the Gutenberg secret is called something to do with precious metals, smithing, and founding. It could be a Smiths and Typefounders Union. Something like "The Worshipful Company of Smiths and Tyhpefounders," or "The Revered Font of Gold and Metal Workers," or "The Secret Council of Engravers and Fontographers."

Isaac Newton believed in the medicinal properties of taking a little Mercury internally each day. I'm guessing that a little heavy metal in the guildmember's diet would be appropriate.

So there would have to be an initiation ritual, obviously. There are lots of different examples of these to draw from. In addition to initiation there is the "Bringing of the Book," the "Inking of the Mark," and the "Taking of an Apprentice." Those four will do for starters. At least one of these includes a communion with ink; one involves tatooing; one involves invocations and presentation of a reading from an ancient book.

Regarding the initiation:

Special rituals and requirements for new members of a group are called initiation rituals. Many social organizations are quite demanding of new members. Anthropologists have a term—mortification rituals—for initiation ceremonies that inflict pain or humiliation or otherwise mortify the new member of the group. To mortify is, literally, to threaten death, and mortification rituals often threaten death either actually or symbolically.

What are mortification rituals? For example, in the initiation ritual for the Freemasons, the candidate is blindfolded and then led around by a rope around his neck. As the candidate approaches the oath of secrecy, the sharp point of a sword is place against his left breast. The Skull and Bones secret society at Yale puts a new member into a coffin. Members chant at him and he is "reborn" into the society.

Mortification rituals encourage the comraderie that results from shared experiences of hardship, familiar to any war veteran. Also, as implied by cognitive dissonance theory, people who sacrifice for a group are more likely to adopt a positive attitude toward the group. Once they have engaged in behavior that implies that group membership is worth paying a high price, they are likely to convince themselves that group membership is very valuable. To feel otherwise would make it hard to explain why they went through the trouble and discomfort involved in joining the group.

Mystery also plays a role in group cohesion. When a new member is recruited to a "secret society" or similar organization, promises are shared, oaths recited, sacred responsibilities pronounced and accepted. Access is allowed to secret writings or places.

Consider the typical graduation ceremony at a college or university. Students and faculty in long flowing robes listen to speakers make weighty pronouncements. Dignitaries hand out scrolls. It is an echo of ancient rites signifying initiation into a guild consisting of the educated elite.
Initiation Rituals

For information on Masonic ritual (old) see Duncan's Masonic Ritual