I've been participating on a henna forum recently. I mainly go to it to get design ideas, ask questions about essential oils, and see other people work. There are so many talented people that post on that site, mashallah.
When I first joined the site, I noticed there were a few other Muslim henna artists so I decided I would ask for their help with how to deal with a few issues I was concerned about. I submitted a post with a few questions to the other Muslim artists. I asked them 3 things
1. How do you deal with not being able to henna men? (I have a festival coming up and I wondered if I should post a sign saying women and children only)
2. How do you deal with not doing images of animals or people in your designs?
3. How do you deal with not doing religious symbols in your designs?
I didn't exclude the non Muslims, and actually said they could give advice as well. I did get some confused responses from non Muslims about not henna'ing men. They said that they had done bridal henna for Muslims where the groom also had them put henna on them. I explained that not all Muslims follow the rules, but in general we should not be touching or be touched by the opposite sex that is not a member of our family.
What shocked me was a response from an artist that said she was Muslim. She posted