  We have analysed optical spectra of two of the hydrogen-deficient knots (J1 &
J3) in the born-again planetary nebula Abell 30, together with UV spectra of
knots J3 & J4. We determine electron temperatures in the knots based on several
diagnostics. The [O III] nebular-to-auroral transition ratio yields
temperatures of the order of 17 000 K. The weak temperature dependence of the
ratios of helium lines at 4471, 5876 and 6678 Angstroms is used to derive a
temperature of 8850 K for knot J3 and 4600 K for knot J1. Ratios of O II
recombination lines, which directly measure the temperature in the coldest
regions of the knots, are used to derive temperatures of 2500 K for knot J3,
and just 500 K for knot J1.
  We calculate abundances both from collisionally excited lines and from the
well-observed recombination spectra of C, N, O and Ne ions. The forbidden line
abundances agree well with previous determinations, but the recombination line
abundances are several hundred times higher. These results confirm the scenario
proposed by Harrington and Feibelman (1984) in which the knots contain a cold
core highly enriched in heavy elements. Forbidden lines are almost entirely
emitted by the hot outer part of the knot, while recombination lines are
emitted predominantly from the cold core. The C/O ratios we derive imply that
the knots are oxygen-rich, contrary to theoretical predictions for born-again
nebulae (Iben et al 1983).
