I want to put in a date and serial number that would be difficult to erase or change. Is it better to print in the number or engrave it in with a laser engraver.

Material will be anti-bacterial PLA.

It will be on free masks donated to schools, I want to make sure we can identify them when they show up at the market or in shops.


For this specific application, it may be better to think in terms of a Lot Number for each batch instead of individual serial numbers. This will still let you trace back an item for where it was originally allocated, and greatly simplify your processing.

Under this plan, you create the STL file for the basic part and before each printing batch open the base file in even a simple tool like MS 3D Builder or TinkerCAD to emboss your number and the date, re-slice, and print.

I actually recommend a deboss here, where the text is recessed into the piece instead of extended outward. In this way it will be more difficult to file away without damaging the part, and again, even the basic modelling tools can quickly customize an STL file in this way.

If you really need individual serial numbers, design the part with a basic recessed rectangular cutout and print these in bulk. Then print individual plates the exact size (very slightly smaller) than the cutout with the serial number and date debossed, and superglue the plates down.

Finally, be aware there's a limit to how small the text can be, based on the size of the nozzle and the capabilities of the printer, and you may find it difficult to print very small text.


It's plastic. Nothing is difficult to remove, but it could be difficult to remove without damaging the functionality of visual quality of the part. If you want to be really devious, you could embed the serial number in an inaccessible cavity inside the print that's not visible without breaking it open.

However, I wonder if it would make more sense to drop this. If you're worried about students (?) or educators (?) stealing and reselling these items, does having a way to trace and punish them really benefit anyone? Even before you consider the harms from doing so, isn't the effort spent tracing (and even the effort automating generation of STLs with each serial number and slicing each one to print individually, rather than using a single gcode job) greater than the value of the item you're worried about losing?

  • $\begingroup$ What type of masks are you talking about? $\endgroup$ Nov 25 '21 at 3:35
  • $\begingroup$ like this againstcovid19.cern/articles/… $\endgroup$
    – Kilisi
    Nov 25 '21 at 3:46
  • 1
    $\begingroup$ Those are silicone masks produced from a printed mold, not printed masks. It was generally determined early on in the pandemic that hard plastic printed masks were not a viable health measure. They can't be made air tight or comfortable to face, and with gaps are less effective than regular cloth masks. $\endgroup$ Nov 25 '21 at 12:39
  • $\begingroup$ no idea, just posted the first one I got from google that had the filters. the mask my daughter found is 3d printed, I'd try and find it, but not relevant to the question $\endgroup$
    – Kilisi
    Nov 25 '21 at 12:43
  • $\begingroup$ OK, well if you did want to do molds like in the thing you linked, that would be an added complication for the serial numbers, since you'd need a way to change out the number each time you used the mold. Anyway, the reason I asked what kind of mask is that I have no idea what a viable 3D printed mask would look like, and that affects how you might viably be able to put identifying information on it. $\endgroup$ Nov 25 '21 at 13:03

Have you considered using a barcode rather than text. It would be easier to print clearly as there are no curves, and would be machine readable.


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