Thanks for the excellent input John!

The German letter that looks like an upper-case B is referred to as an ‘ess-zed’. It has been replaced among some German speakers by ss, especially in Switzerland. As the German name of the letter indicates, it was originally a combination of sz, not ss. Some older printed texts actually used sz, but this practise has fallen out of favour since World War II. Recent attempts by German authorities to retire the letter altogether generated considerable push-back, and may ultimately fail.

I presume the letter Eth fell into disuse due to its visual similarities to the letter D (Ð/ð D/d) on the page. I presume its successor, the letter Thorn (Þ/þ) suffered the same fate for a similar reason since it is so visually similar to the letter P/p, just like the letter Wynn (Ƿ/ƿ). Above you mentioned confusion caused by such visual similarities to other letters as the reason, or at least part of the reason for a some of these letters to fall into disuse, notably Wynn (Ƿ/ƿ) compared to P/p, Yoghurt (Ȝ/ȝ) compared to the letter Z/z when written in cursive, and Long s (ſ) compared to the lowercase f, which all make perfect sense. You did not comment on such similarities to other written or printed letters as a contributing reason for why Eth & Thorn (or Eð & Þorn) however. I am curious to know if my presumptions about their falling to disuse for the same reasons are correct. Is it known why Eð & Þorn stopped being used, and if so am I correct as to why?

A question you may have inadvertently left open, regarding thorn and eth. It was my belief that thorn was the voiceless dental fricative, (as in “think”), and eth the voiced (as in “the”). This is supported by the similarity of the eth character to Latin upper-case D and to Greek lower-case delta, also voiced. This is controverted by the use of thorn to spell the definite article, which is voiced.
Another site states that thorn is voiced and eth voiceless. Your site describes them both as voiced. Seems a voiceless dental fricative is needed. What Þink you?

Hey drive by commenter (love the name btw) Ampersand is covered over in my other post: Typing Through Time: Tracing the Roots of Common Keyboard Symbols (https://calligrascape.com/keyboard-symbology/).

Yes, you are correct, long s is used in German still, but from an English perspective, it is “forgotten”.

Thank you for your comment

Long s still is used in German.

þats great! þanks for letting me know!

Hi Vell!

I am very glad you enjoyed this post. It seems to get more traction that I would think. I do in fact have a post about the common keyboard symbols (which includes ampersand) that for some reason I did not link to. Thank you for that, as I will now link to it here as well: https://calligrascape.com/keyboard-symbology/

If you are interested, there is a good comment listing a whole bunch of new letters that I will be looking into in the future. That could be a good place to start 🙂

Let me know if you find any information and I will add it to this post.

Golly, you made my week! I love such comparative rarities. Roughly half a dozen were new and surprising.
In my Jitterbug 4 phone, a mixed blessing, I saw only a few “tofu” (See origin of the Noto fonts).

Right in my immediate neighborhood is a small plumbing company named for (quite likely) its founder. I see its panel trucks, showing “Æ Carter…” prominently, as the company name.
Alas, while (Ash) Carter was a national Cabinet secretary, I failed to publicize the close similarity.

I’ve found it difficult in past

decades to learn the same of “Œ”, and when I did, it was a modest surprise.

It would be a delight to read more about the the origins (if known, of the letter, as well as its name) of more of these.
Probably the origin of the contraction “ampersand” (which you alluded to) is best known. One such explanation said that it used to be the last letter (27th) of our alphabet.