If you dye MJF parts or vapor smooth them, you’re solving two different problems. “What’s the best smoothing for MJF PA12?” comes up on Reddit again and again, and customers ask bureaus the same thing in plainer terms: can it be black, smooth, or waterproof? Dyeing and vapor smoothing solve different problems. Knowing which one a customer actually needs saves remakes and quoting mistakes.
What does dyeing actually do?
Dyeing changes color and nothing else. MJF PA12 is already dark grey from the fusing agent, so a black dye takes it to an even, deep black. RYSE 3D, a UK finishing provider, notes that dyeing adds no wall thickness and reaches internal geometry. It also says dyeing doesn’t close porosity, so a dyed part is no more watertight than an undyed one.
What does vapor smoothing do?
Vapor smoothing seals and smooths the surface. Shapeways describes its MJF Black Smooth finish (AMT’s PostPro process) as smooth, semi-shiny and watertight, reaching internal cavities with no more than 0.4% dimensional change. Nylon can’t be smoothed with hobby solvents like acetone, which is why commercial PA12 smoothing uses dedicated equipment and chemistry. The Reddit thread makes the same point.
Should you dye MJF parts or vapor smooth them?
- Only needs to look black: dye.
- Needs to seal against fluids, resist dirt, or feel smoother: vapor smooth.
- Needs both: a common production route is bead blast, vapor smooth, then dye (RYSE 3D).
Any MJF-specific advantage?
Yes. Because the MJF core is grey, a scratch on a dyed part shows grey, not white. That makes wear less visible than on dyed white SLS nylon.
How should this show up in your quote?
Treat each finish as its own priced operation with its own lead-time impact, especially when vapor smoothing goes to an outside vendor. Ask the customer’s real requirement (“does it need to hold water?”) on the quote form rather than by email, and track each finishing step separately in your MES so you can see where finished parts are waiting.
Related on the Solvi blog: MJF Watertight Parts: Can PA12 Hold Water Under Pressure?; Depowdering SLS and MJF Parts: When Is Automation Worth It?.
Sources: RYSE 3D black dyeing guide; Shapeways Black Smooth PA12 article; RapidMade MJF vs SLS surface finish analysis; r/3Dprinting PA12 smoothing thread.