Abstract. We strengthen Gabber's l ′ -alteration theorem by avoiding all primes invertible on a scheme. In particular, we prove that any scheme X of finite type over a quasi-excellent threefold can be desingularized by a char(X)-alteration, i.e. an alteration whose order is only divisible by primes noninvertible on X. The main new ingredient in the proof is a tame distillation theorem asserting that, after enlarging, any alteration of X can be split into a composition of a tame Galois alteration and a char(X)-alteration. The proof of the distillation theorem is based on the following tameness theorem that we deduce from a theorem of M. Pank: if a valued field k of residue characteristic p has no non-trivial p-extensions then any algebraic extension l/k is tame.1. Introduction 1.1. Background. This paper falls within the area of resolution of singularities by alterations, so we start with a brief review of known altered desingularization results.1.1.1. de Jong's theorems. In [dJ96, Theorem 4.1] Johan de Jong proved that, regardless of the characteristic of the ground field, an integral variety X can be desingularized by an alteration b : X ′ → X, i.e. a proper dominant generically finite morphism between integral schemes. In addition, given a closed subset Z X one can achieve that Z ′ = b −1 (Z) is a simple normal crossings (snc) divisor, and f can be chosen G-Galois in the sense that the alteration X ′ /G → X is generically radicial, where G = Aut X (X ′ ), see [dJ96, Theorem 7.3]. de Jong's altered desingularization was the first resolution result that applies in such generality and it immediately found numerous applications. Also, de Jong proved an altered version of semistable reduction for an integral scheme X over an excellent curve S, see [dJ96, Theorem 8.2]. The latter can be viewed as altered desingularization of morphisms f : X → S with S a curve. IT14b]. The most recent and powerful advance is Gabber's l ′ -altered desingularization: it is proved in [IT14b, Theorems 2.1 and 2.4] that if l is a prime invertible on X then one can achieve that the degree [k(X ′ ) : k(X)] of the alteration b is not divisible by l both in the altered desingularization and altered semistable reduction theorems. This extended the field of applications of altered desingularization to cohomology theories with coefficients where l is not inverted, for example, Z/lZ or Z l .