Came across this today:
《廣韻·平·江》：“𧜧，短敞衣也，丑江切。”
𧜧 has MSM pronunciation chuāng but if we take 丑江切 that means we have ch + iang = chiang.
Other characters with 丑江切 seem to include:
䚎 (MSM: also chuāng)
憃 (MSM: chōng)
广韵 isn't exactly modern and 丑江切 seems to come out differently in different cases today.
What I'm mainly curious about here though is:
Did (modern) Mandarin Pinyin chiang used to exist?
The 反切 in 廣韻 use Middle Chinese pronunciation, so one cannot take the modern readings of the 反切 上下字 as a guide to how a word might be pronounced.
In this case, you are looking at words in the 江 rhyme category. These words have developed a -j- medial in Mandarin (when there is a velar initial) that was not present in Middle Chinese. Other dialects have not. Compare, for instance, the Cantonese pronunciation of 江 "gong".
Although 𧜧 is not a "living" character, words which are in the same initial and rhyme categories are still around, such as 撞 zhuang. This is the regular development.
Mandarin has never had retroflex initials followed by medial -j-; in fact, this would seem to be a very unlikely combination in any language.
Most words with Mandarin initial zh, ch, sh, or r had a medial -i- in Middle Chinese. (If you know about 等 "division," modern zh, ch, sh, r come from divisions II and III, with III being more common.)
So, if you read the old dictionaries naively, you will expect to see "shiao" "zhiang" "rin" and so forth. The -i- was lost on the way to Modern Chinese.
It seems that there were sounds like "chiao" in the Zhongyuan Yinyun (from 1324). For instance there was a difference between 抄 (chao) and 超 (chiao). (You can look up ZYYY and more on zdic.net -- but realize that the romanizations are the work of modern scholars.)
You can also see evidence of the -i- in Cantonese, where for example 张 is pronounced the same as 将.
You have to specify what you mean.
If you mean the actual sound -- yes, it happens to have existed.
If you mean whether the sound existed in the history of Mandarin, not Middle Chinese -- yes, it happens to.
If you mean whether at some point the character 䄝 was pronounced like Modern Standard Mandarin chiang, uh probably not.
To go through some Middle Chinese reconstruction details, 丑 has onset 徹 in MC, reconstructed as *[ʈʰ], and 江 belongs to the final group 江, reconstructed as *[ɰɑwŋ], and has the "Level" tone. So in (my version of) the MC reconstruction, 䄝 was pronounced something like *[ʈʰɰɑwŋ] in some stage of (early) MC.
Now, this syllable eventually became MSM chuang1 through sound changes. But if you are wondering what happened to something close to *[tʂʰiɑŋ], the medial [-i-] became [-u-] in that particular position and became MSM chuang as well.
You might wonder what the heck happened so that you get superficially in MSM ch + iang = chuang in this case.
The onset 徹, reconstructed as a stop in Early MC, entirely became an affricate *[tʂʰ] at some point (and merged with the existing retroflex affricates). This is why you don't see this sound change superficially.
The final 江 developed differently depending on the conditions. In any case it was completely merged with the final set of 阳 *[ɑŋ]. The medial *[-ɰ-] disappeared in most cases, but turned into a [-u-] after retroflexes in Mandarin, and, distinctively, developed into an [-i-] after dorsals (i.e. velars, and glottals if your reconstruction has them) in historical Northern Mandarin dialects. Now, the character 江 happens to have a dorsal onset 见 *[k-] (velar), so the medial *[-ɰ-] there turned into [-i-], which, by the way is how you've got the palatalized onset j.
