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Technical Insert · Volume I
The protocol.
How a tattoo gets onto Solana: Bubblegum V2 + Token-2022 + a very stubborn Merkle tree.
01 / The Flow
Chair to chain,in five steps.
Every mint passes through the same sequence — the only thing that differs between walk-ins and enterprise issuers is which Merkle tree receives the leaf.
- Step 01
Wallet walks in
User connects a Solana wallet and picks a flash from the sheet. Selection is stored locally until signature.
- Step 02
Backend prepares the needle
POST /api/mint/prepare builds a Versioned Transaction with Bubblegum V2 mint, Token-2022 non-transferable flag, and partial sig from mint authority.
- Step 03
Wallet signs once
User signs. No blind approvals — credential, recipient, and tree are in plain view. Signed tx sent to POST /api/mint/confirm.
- Step 04
Helius lands the mint
Server submits via Helius RPC. On confirmation, cNFT leaf lands in the shared Merkle tree, DB stores the metadata pointer, Redis cache invalidates gallery.
- Step 05
Ink is permanent
Credential is now soulbound. Transferability is blocked at the mint level. Revocation requires tree authority (enterprise issuers only).
Mint Flow Diagram
02 / The Bill
Cost per tattoo.
Standard SPL NFT
$2.00
per mint, excluding IPFS
~ 0.012 SOL
Metaplex cNFT (INKD)
$0.0005
per mint, Bubblegum V2
~ 0.0000028 SOL
10k Issuance Cost
$5.00
fits on a petty cash slip
~ 0.028 SOL
| Metric | SPL NFT | INKD cNFT | Delta |
|---|---|---|---|
| Mint cost | $2.00 | $0.0005 | 4000x cheaper |
| Transfer? | Yes | Blocked | Soulbound |
| Storage | Rent-exempt SOL | Merkle leaf | ~0 bytes |
| 10k batch | $20,000 | $5.00 | 99.97% save |
| Read latency | 100–300ms | <200ms DAS | same |
03 / The API
Endpoints,straight up.
Hono on Node on Railway. JSON in, JSON out, Zod validated, Redis ratelimited. Nothing fancy — fancy loses in production.
POST/api/mint/prepareBuild a signed mint tx↓
curl -X POST https://api.inkd.fun/api/mint/prepare \
-H "content-type: application/json" \
-d '{"wallet": "...", "credential": "first-time"}'POST/api/mint/confirmSubmit signed tx + persist record↓
curl -X POST https://api.inkd.fun/api/mint/confirm \
-H "content-type: application/json" \
-d '{"serializedTx": "base64..."}'GET/api/galleryLatest 100 cNFTs (Redis cached)↓
curl https://api.inkd.fun/api/galleryGET/api/gallery/:walletPer-wallet ink history↓
curl https://api.inkd.fun/api/gallery/WaLL3TPuBKey...POST/api/verifyMerkle-proof ownership check↓
curl -X POST https://api.inkd.fun/api/verify \
-H "content-type: application/json" \
-d '{"cnft": "INK...", "owner": "..."}'POST/api/issuer/register2nd hook: onboard an issuer↓
curl -X POST https://api.inkd.fun/api/issuer/register \
-H "authorization: Bearer $INKD_KEY"POST/api/issuer/batch-mint2nd hook: bulk attest↓
curl -X POST https://api.inkd.fun/api/issuer/batch-mint \
-H "authorization: Bearer $INKD_KEY"OpenAPI spec lives at /openapi.json (after backend deploy).
Tree
Merkle
max_depth 14, max_buffer_size 64. 16,384 leaves per tree. New trees auto-provision once full.
Token
Token-2022
Non-transferable extension. Frozen delegate. Revocable by tree authority when required.
Metadata
IPFS + DAS
nft.storage for artwork + schema. Helius DAS for read path. Everything mirrored in Postgres for fast UI reads.