but perhaps of more interest is this:

Un- is freely prefixed to adjectives of all kinds, except where a Latin form in in-, etc., has definitely established itself in common use. Both forms, however, may co-exist, and in some cases a new formation with un- has been introduced when that with in- has acquired a connotation which it is desirable to avoid. The form with un- is then purely negative, while the other may have almost a positive sense, e.g. un-moral in contrast with immoral. (When the form with un- has similarly acquired a positive implication, the simple negative or neutral sense is expressed by the use of non- or not-.) There is also considerable restriction in the use of un- with short simple adjectives of native origin, the negative of these being naturally supplied by another simple word of an opposite signification. There is thus little or no tendency now to employ such forms as unbroad, undeep, unwide, unbold, unglad, ungood, unstrong, unwhole, unfew, etc., which freely occur in the older language. On the other hand, derivative forms in -al, -ant, -ar, -ary, -ent, -ful, -ic, -ical, -ile, -ish, -ive, -ly, -ory, -ous, -y, etc., are too numerous to be completely recorded. The general character of the less usual or permanent of these and other adjectival forms is illustrated by the following examples, which are a severly restricted selection, and could be indefinitely increased by the addition of less noteworthy material.
In dictionaries of various dates many formations are given of which no real instance has been found. Levins (1570) has unhateful, unprecious. Florio (1598 and 1611) renders equivalent Italian words in in- by such forms as unavailful, unbrittle, uncontinuall, uncoy, unempty, unfrail, unnice, unoffensible, unopen, unplenteous, unshrill, unvalorous. Ash (1775) gives unalphabetical, unattendant, uncohesive, uncompatible, uncompressible, uncompulsive, etc. (about 80 in all). Later dictionaries (Webster, Worcester, etc.), with or without indication of source, have the entries unabundant, unbiographical, uncogent, uncollectible, undeceptive, undeliberative, etc.
Recent formations include: unadult, un-African, unairworthy, unambivalent, unarcadian, unarchæological, un-Australian, unbitchy, unblameworthy, unblasé, unbureaucratic, un-Byronic, uncerebral, uncharismatic, unchic (also absol.), un-Chinese, unchipper, unchoosy, un-Christmassy, uncomfy, uncomposite, uncomradely, unconscient, uncool [esp. cool a. 4e] (also absol.), uncooperative, uncosy, uncranky, uncreditworthy, uncuddlesome, uncuddly, un-Darwinian, undeducible, un-Dickensian, undimensional, undisastrous, undoctrinaire, undynamic, unecological, uneconomic, unecstatic, unecumenical, unegoistic, unegotistic, unegotistical, unerotic, unetymological, unexotic, unfaery (poet.), unfeline, unfeminist, unflamboyant, unflashy, unfond, unfresh, unfurtive, un-Gaelic, ungay, ungimmicky, unglamorous, ungroovy, unhep (also absol.), unhip (also absol.), unhors(e)y, unideological, unintrospective, unirksome, unironic, unironical, un-Islamic, un-Italian, un-Jamesian, un-Japanese, unjingoistic, unkeen (also absol.), unkosher, unlegendary, unlocal, unmarital, un-Marxist, unmawkish, unmeritocratic, unneurotic, unodoriferous, unopen, unpacifist, unphonemic, unphon(e)y (also absol.), unphotogenic, unplatonic, unpolemical, unpolicemanly, unpositive, unprestigious, unpriggish, unprivate, un-Proustian, unpugnacious, unradiogenic, unresilient, unrevolutionary, unrisky, unroadworthy, un-Russian, unscenic, unseductive, unselective, unsemantic, unsexy, un-Shelleyan, unsnobbish, unsorry, un-Spanish, unspecial, unspectacular, unstarchy, unsterile, unstiff, unstuffy, unsycophantic, unsymmetric, untendentious, untense, untherapeutic, unthistly, unticklish, untogether, untouristy (also absol.), untraditional, untrendy, unurgent, unutilitarian, unviable, un-Victorian, unviolent, unvisual, un-Western, un-with-it, unworthwhile, unyoung.


[usage examples abound]