Flash X-ray pictures of gap test arrangements show that the material of the gap, in this investigation disks of plexiglass, will disperse and destroy unconfined acceptor charges, if the shock is not strong enough to get a prompt or at least a very fast initiation. The initiation location and/or the direction of the detonation wave of the donor charge to the gap material and acceptor charge or inverse, is under the investigated test conditions from very small influence to the behaviour of the acceptor charge.