Hi Lothar,
The weight is possibly by Salvador Ysart and yes, it was probably made in the Ysart Brothers (Vasart) period. The only way I know of deciding whether an unsigned and unlabelled weight is earlier or later Vasart is by UV testing (or perhaps Specific Gravity tests). But there is still the problem that some weights that appear to be earlier (style and canes) could have been made in the Strathearn years as the UV result for later Vasart and Strathearn periods is the same!
However, the way that weight is finsihed to the base suggests to me the hand of Salvador.