So yes, mink lashes are vegan and cruelty-free, and have nothing to do with animal mink. While the use of fur coats has become controversial in recent years due to growing concern for animal welfare, beauty enthusiasts have largely ignored the use of mink lashes, which are by no means free from animal cruelty. The word “mink” tends to confuse many eyelash artists and clients, and many of them tend to believe that eyelashes are made from animal hair. What makes mink lashes — by definition a toiletries item — an even more questionable purchase is the fact that European minks are in serious danger of extinction.
For the same PBT mink eyelash extensions, some eyelash brands would call it mink, while others would call it real sabre. Once you know this information, you can't justify exploiting these animals just to produce toiletries such as false eyelashes. There is absolutely no need to contribute to the suffering and death of animals to achieve a certain look, as there are a variety of cruelty-free options when it comes to eyelash extensions, and many are able to replicate the light and faint feel of the animal version. Good art stores should be able to advise you on the best vegan-friendly brush for your project, and also help you avoid other animal-based materials, such as squid inks and charcoal.
In any case, mink lashes are very unlikely to come from “brushing”, and much more likely that they were obtained from animals that were killed for their fur. Eyelash extensions are sometimes made of mink fur, and yes, they likely come from animals incarcerated on the same miserable, dirty fur farms that supply the fashion industry.