While you are buying a liquid blue, you should know what you are buying? There are very popular brands which are not blue at all but dyes and do not have the properties which a whitner should have, they may be good for first few washes but in longer run bound to harm the cloth, whereas liquid blue formulations based on blue are less harmful to cloth and the hands. But best to use is powder blue which is one of the safest and best product, though usage is slightly difficult but the trouble is worth taking for the sake of performace, safety and quality and best of the lot is the Robin, I strongly recommend its use for post wash.