You can create your own waiver as long as you add in all the necessary topics of a brow PMU waiver or you can buy one online from websites such as Etsy and edit the form to your liking.
After I work on each client, I like to chart down their name, date, time, and pigments I used along with anything I will need to pay attention to at their next visit. For example, how did the pigment mix I used heal on their skin? Did I understand their undertones correctly. Maybe my client had very obvious asymmetry or they had orange skin. Making sure you write down something positive and something you can improve on as a beginning artist will greatly help you becoming a more aware artist.
