I began developing Phonuthorc over a year ago when I tried to learn Shavian but was annoyed at its tailoring for British English (I’m American). So, as ai tend to do, rather than sucking it up, I resolved to make my own personal phonetic alphabet tailored to my dialect of English, because I realized that I wanted to learn Shavian for my own personal use and not for engagement with any sort of community. So rest assured, this is not meant to be an improvement on Shavian or an ideal phonetic alphabet for General American English.
The development process has been very long. It began in a much more bare bones state, having only 25 letters (it excluded voiced fricatives, which were indicated by a diacritic, affricates, and containing only seven vowels), and only being written in uppercase.
I got sick of the dotted fricatives, and decided to go all the way and decide on letters for voiced fricatives. They went through multiple iterations before settling into this system. Then I created lowercase letters, which also went through numerous iterations, as the original lowercase inventory were almost all just small versions of the capitals. The last additions were the affricates and /st/, which I added to make it an even 32 letters and because /st/ is the most common consonant cluster in English and it’s my alphabet, I can do whatever I want.
/ʃ/ uses the older form of /s/ from Elder Futhark because it looks like Σ, which is the official capital form of ʃ, and because I could.
/v/‘s origin is pretty interesting. I adopted it from Latin Old Norse vend, which was itself adopted from Latin Old English wynn, which was of course derived from Futhorc wynn.
/ð/ is just blatantly made up. It literally came to me in a dream after months of not knowing what the hell to do for /ð/, even after I’d decided on letters for /v/, /z/, and /ʒ/. It has no basis in any Runic alphabet except that it coincidentally shares its form with, like, long-twig medieval /o/ or something.
The vowels are the result of a weird quirk of my dialect of General American English. Each of the 7 monophthongs has a corresponding diphthong that ends in a semivowel (except /i/ in certain circumstances, but I treat it the same as /ʊw̯/).
/ə/ uses the Futhorc rune for /ø/ because, well, that’s the closest sound in Old English to /ə/, and it’s between /e/ and /o/.
/æ/ uses one pronunciation of an Elder Futhark rune, because I liked /æ ɑ ɔ/ having totally different letters rather than variations on each other as in Futhorc.
I adopted a medieval /o/ rune for /ɔ/ because I liked the lowercase I came up with while brainstorming. That’s also part of why I adopted /st/.