Design Problem
The aim of the IPA is to provide a unique symbol for each distinctive sound in a language. Although some of its glyphs are unrelated to any standard alphabet, most characters are direct derivatives of characters of the Roman or Greek alphabets, so when designing IPA glyphs, it is tempting to reuse the previously-designed Roman and Greek glyphs to save time. Some of these Roman and Greek derivatives have been rotated 180 degrees, which maintains the contrast of thick and thin, but some are mirrored, which results in incorrect weight distribution, making the glyphs appear inconsistent with the rest of the set. It is worth noting that the first (metal) IPA typeface (Passy 1888) does not include any mirrored characters. Earlier phonetical alphabets use more accented characters (Lepsius 1863), later ones introduce many new derivative glyphs (Pallum and Ladusaw 1986). It seems that the introduction of flipping reflected the development of either photocomposition or early digital technology.
The writing systems which have developed to represent various languages are artificial, and there is no direct relationship between the spoken and written forms of a language; the relationship is instead conventional or learned. This is why most linguists ignore writing. Fellow type designers I have spoken with also consider phonetic fonts to be artificial, and therefore do not apply the same criteria (such as weight distribution and legibility) to the design as when they make text fonts. Though there are a number of phonetic fonts, I have found only one which treats phonetic glyphs independently, as letters on their own. Gentium, a very complete multilingual font designed by Victor Gaultney fixes some reversed glyphs, but does not include a complete IPA set. Fedra Serif Phonetic treats the IPA glyphs as individual letterforms and is drawn according to the same principles as Fedra Serif. This approach makes them clear and readable forms in themselves, making subtle weight corrections to create a more typical contrast pattern. This solution seems logical, seeing that many linguistic grammars use a large quantity of material typeset in IPA, in which harmony of form is important for improved legibility. In this context the IPA is not deciphered symbol by symbol but read as continuous text. Furthermore, numerous IPA characters are also integrated into orthographies of natural languages, especially in Africa, so there is a possibility that people may use these fonts for regular text setting.