The Collaborative International Dictionary of English v.0.48:

Inartificial \In*ar`ti*fi"cial\, a. [Pref. in- not + artificial:
   cf. F. inartificiel.]
   Not artificial; not made or elaborated by art; natural;
   simple; artless; as, an inartificial argument; an
   inartificial character. -- In*ar`ti*fi"cial*ly, adv. --
   In*ar`ti*fi"cial*ness, n.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

92 Moby Thesaurus words for "inartificial":
   arcadian, artless, authentic, bona fide, bucolic, candid,
   card-carrying, dinkum, direct, following the letter, genuine, good,
   homespun, honest, honest-to-God, in the raw, ingenuous, lawful,
   legitimate, lifelike, literal, naive, native, natural,
   naturalistic, naturelike, original, pastoral, pristine, pure, real,
   realistic, rightful, rural, simon-pure, simple, sincere, sterling,
   straightforward, sure-enough, true to life, true to nature,
   true to reality, unadorned, unadulterated, unaffected,
   unartificial, unassumed, unassuming, uncolored, unconcocted,
   uncopied, uncounterfeited, undesigning, undisguised, undisguising,
   undissembling, undissimulating, undistorted, unembellished,
   unexaggerated, unfabricated, unfanciful, unfeigned, unfeigning,
   unfictitious, unflattering, unimagined, unimitated, uninvented,
   unpretended, unpretending, unpretentious, unqualified, unromantic,
   unschooled, unsimulated, unsophisticated, unspecious, unspoiled,
   unstudied, unsullied, unsynthetic, untouched, unvarnished, verbal,
   verbatim, veridical, verisimilar, virgin, virginal,
   word-for-word