There is no credible historical evidence, whatsoever, of Tibetans ever having used singing bowls.
The Tibetan singing bowl doesn’t exist and isn’t real, but the racist mythologization of Tibetan people most definitely is.
For the sake of our collective sanity, it’s worth spreading far and wide recent exposés debunking the myth of “Tibetan singing bowls”. Two online articles are especially relevant, by Tenzin Dheden and Ben Joffe—do please share!
The orientalist fetishisation of the Mystic East comes into its own with the suspicious package of New Age healing, meditation, and “spirituality”, of which the bowls makes sonorous emblems. 
In recent decades, through shrewd marketing they began appearing in curio shops and New Age boutiques—and Tibetan refugee stalls. Fed by Google, Twitter, and Amazon, the myth just won’t go away—a field day for muddled hippies, along with crystals and chakras. Don’t get me wrong—do what you like (It’s A Free Country—Oh, hang on…): just don’t pretend they’re part of Tibetan ritual practice. Or that they’re “ancient”.
As Tenzin Dhoden observes:
This Western practice of essentializing Tibetan culture and capitalizing on that cultural commodification forces marginalized Tibetan refugees into a tricky situation—they get the economic opportunity to sell some metal bowls to fascinated white people but at the cost of being a willing participant in the orientalist imagination of Tibetanness, which in turn causes great cultural trauma and pain to the Tibetan people.
Eager hippies are undeterred by the lack of evidence—Joffe notes:
Tibetans’ silence or disavowals of knowledge are interpreted in three typical ways:
1) the Tibetans to whom the author spoke were not privy to the deepest secrets of their own culture, and therefore unable or unqualified to speak
2) These Tibetans had forgotten or lost the secret knowledge of which the bowls are a part, or
3) These Tibetans are hiding something, guarding their knowledge from prying outsiders or for fear of persecution by ‘orthodox’ Buddhist authorities.
He refers to a passage by “French-Belgian anarchist-feminist-opera-singing-esotericist-explorer” Alexandra David-Néel (1868-1969), that turns out not really to support the hippies’ argument. And he cites Robert Beer:
Brass or bronze bowls first began to appear on Tibetan refugee stalls during the 1970s, but these objects were actually the eating or offering bowls of these impoverished refugees. Over the last few decades, these Tibetan singing bowls have been widely manufactured for the tourist markets of India and Nepal, but stories of their employment in ancient Tibet as mystical musical instruments are a modern myth.
The bowls seem to have made their debut in a 1972 recording by Henry Wolff and Nancy Hennings. Joffe cites Choetso Amnyetsang on Miley Cyrus, and Austrian anthropologist Agehananda Bharati’s “pizza effect”. He ends on a tolerant, nay enlightened, note:
As Tibetans continue to discuss the potential meanings and consequences of these sorts of cultural commodification pizza-effect-meets-cultural-appropriation scenarios, singing bowl enthusiasts continue to strongly resist acknowledging their own “off-label” use of the bowls. As an anthropologist, rather than throw down some gauntlet and declare that singing bowls are or aren’t Tibetan, I would much rather focus on the complicated social and political lives of these deceptively mundane/deceptively sacred objects. If the anthropological literature on religious movements has taught us anything it’s that cognitive dissonance need not spell disillusionment and cosmological collapse. Rather, cognitive dissonance, epistemic “murk”, and excess themselves spur reformulation, and promote innovation, religious creativity, and change. Which totally feels like a vibe anthropologists can get into.
Tenzin Dheden is more candid:
If you find “sound baths” healing, great! Good for you! But if you can, however, please kindly stop mythologizing and exoticizing Tibetans, and leave us out of your pseudo-scientific New Age nonsense. We are quite preoccupied resisting China’s violent settler colonial rule and fighting to preserve our rich cultural heritage as it is.
Not only are the bowls doing a disservice to Tibetan culture generally, but they detract from our understanding of the social life of Tibetan ritual and its soundscape of complex vocal liturgy accompanied by drums and cymbals, shawms and trumpets.  Here’s the Lyrichord album Tibetan ritual music (1967):
See also Sister drum.
 For a broader treatment of Western images of Tibet, see e.g. Donald Lopez, Prisoners of Shangri-La: Tibetan Buddhism and the West (1998). “World music” may also take some of the blame. On the bowls, see also here.