An often stated ‘rule’ in the NFT space is that NFTs should not be minted multiple times across different blockchains. One reason given is that doing so would result in different histories of ownership for the NFT :

https://www.quora.com/Can-you-mint-the-same-NFT-on-different-blockchains

Another reason given is that the definition of ‘scarcity’ becomes blurred if it is not clear that an NFT is available on multiple chains (that is, it is a “cross-chain NFT”) :

https://www.reddit.com/r/ergonauts/comments/q0fo1f/minting_the_same_nft_on_multiple_chains/

This blurring of the definition of scarcity can then cause a buyer, who has assumptions about the scarcity of the piece and who then discovers the same piece on a different chain, to give you (the creator) a bad reputation :

https://nftplazas.com/learn-about-nfts/sell-the-same-nft-on-different-platforms/

The same point is made in this article, in which the term ‘platform’ appears to mean ‘blockchain’, as distinguished from ‘marketplace’ :

https://nftdesire.io/can-you-sell-an-nft-on-multiple-platforms/

Others, however, point out that minting an NFT on a “different platform” can result in a creator being banned from the platform. This does not make sense if ‘platform’ means ‘blockchain,’ because there is no software-based mechanism by which anyone can be banned from using a blockchain. Only marketplaces (which use blockchains under the hood) could ban users from using marketplaces (not the blockchains themselves), and presumably the terms and conditions of the marketplace would specify when and how this would occur, though I myself have not read any terms which have done so. In fact, the FAQ of a very popular multiple-blockchain marketplace - Rarible - specifically states that they do not enable moving NFTs between blockchains, but that the same effect can be had by minting the same art multiple times on each chain :

https://rarible.com/how-it-works/using-rarible/which-blockchains-does-rarible-support

Despite this alternate definition behind the meaning of ‘platform,’ the avoidance of possibly being banned then becomes another reason given to avoid cross-chain NFTs:

https://www.rennoco.com/post/nfts-minting-and-copyright-what-you-should-know-as-an-artist

Note that at the time of writing, typing the question “can i mint the same nft on multiple blockchains” into the google search engine will result in a quote from the above article (which uses ‘platform’ in the ‘marketplace’ sense), which incidentally is then misattributed to an answer on quora.

Several people are attempting to ease the enforcing of this ‘rule’ by creating tools which allow an NFT to be “moved” between blockchains, such that it would only be ‘unlocked’ on one blockchain at a time :

https://www.finder.com/cross-chain-nfts

Still other investigators recognize that the uniqueness of NFTs is limited to the blockchain on which it is minted and that many people misunderstand this aspect of NFTs, leading to a belief that there is only one “real” blockchain which contains the “real” nft :

https://www.wired.com/story/nfts-dont-work-the-way-you-think-they-do/

In considering this question, a group of Literary NFT creators (that is, creators of NFTs which present poems or other types of literature) note that there are some aspects specific to literary NFTs which further muddy the waters on what is acceptable, given that poems and other literature can be presented in multiple ways - for example, as pure text, or as an audible reading, or as a video overlayed with graphics and the words of the poem as the poem is recited. In this case, is a text version of an NFT poem “equivalent” to the video version of the same poem? What about the same poem being read by different people? Is it ethical, in other words, to mint different presentations of the identical poem as separate NFTs on the same blockchain, let alone across blockchains?

https://open.spotify.com/episode/2AduDPqIfsnpixd163eN3K

One of the conclusions reached by the podcast was that as long as the buyer is AWARE of the existence of different formats of the same poem and/or other mints of the poem on the same or other blockchains BEFORE purchasing, or is aware of the POSSIBILITY that the scarcity of the item may change in the future, then the acceptability of cross-chain poetry NFTs becomes more palatable, assuming of course that the author of the poem is the same individual or group of individuals which has minted all presentations of the poem on all blockchains in which they are found.

To address these concerns, I have opted to mint my poems on multiple blockchains in the following way :

1. I pick one blockchain (e.g. Ethereum), one format (e.g. Text as a JPEG), and one marketplace that supports the blockchain (e.g. Foundation) upon which to make the first mint, WITHOUT listing it. Within the description of the NFT, I include a link to which potential buyers can go in order to determine the cross-chain scarcity of the NFT (e.g. oddwritings.com/details/february.htm).

2. I determine which other marketplaces end up indexing the NFT automatically after I mint to the chosen marketplace, and then provide links to those marketplaces in a drop down for the user.

3. I verify which of those marketplaces failed to copy over my description of the NFT (which contains the scarcity link), and manually update those descriptions to contain the link.

4. I repeat the above steps for a number of different blockchain/format combinations.

5. When I am ready to list, I list the NFT in each chosen marketplace in the currency appropriate for the blockchain, such that at the time of listing the prices are equivalent across blockchains.

6. I repeat step 4, except that I immediately list the NFT for a price which matches the existing prices.

7. As soon as any format of the NFT, on any blockchain, gets sold, I then cease repeating step 4, and update the scarcity link to reflect that the scarcity is now frozen across blockchains.

The above steps provide the benefit of allowing purchasers to pick whichever blockchain / currency / marketplace they prefer, while still understanding the status of the scarcity of the NFT before buying. They also provide the benefit of allowing me, the creator, to broaden my base of potential sales, and they also provide the benefit of helping less popular blockchains compete against more popular ones.

However, there are also some problems with the above steps :

1. The difference in price between the NFT across blockchains, which is initially close to zero in step 6, will increase over time, given that currencies will rise and fall in value with respect to one another. I could mitigate this by accepting payment only in either FIAT or stablecoins; however, this removes the benefit of allowing the purchaser to pick their preferred blockchain / currency / marketplace, not only because it restricts the currency, but also because not all marketplaces allow payment in that manner.

2. Not all marketplaces support providing a description to an NFT (for example, Typed.Art on the Tezos blockchain at the time of writing). I could mitigate this by including a non-clickable link to the scarcity URL within the NFT itself.

The above strategy is therefore obviously not optimal; however, if you also feel, as a writer, that you like the idea of supporting the acceptance of cross-chain NFTs in a way which avoids misunderstandings with purchasers, these steps may give you a starting point on how to go about it, or at least give you some ideas on possibly more effective alternatives.