First layer discoloration  

RE: First layer discoloration

Update:

I contacted PRUSA directly and they told me most likely my slicer settings were a bit off. I printed the same part using a standard Input Shaping profile and I got same result....

RE: First layer discoloration

Are the photos correctly labeled? They seem backward from your description.

Either way, this looks like a multi colored print and it's printing black first. If that is indeed the case, I have had prints come out looking exactly like that (with exactly black then white). In my case, it wasn't even right away, but at some point shortly after switching to the white filament, some black filament left somewhere inside the path to the nozzle started turning the white extrusion grey. Eventually the white became totally white but for a short time there, it was grey and then slowly transitioned back to entirely white.

To fix it, I either print the white first (not always an option), purge a lot more white, or slip an inch or two of "cleaning filament" into the extruder before the white. I don't know if cleaning filament is a gimmick or not, but in my case, it always seems to purge whatever color was previously extruding without anything left behind to affect the next color.

RE: First layer discoloration

Yes you are right the labels in the picture are swapped, my bad! I made 1mm with white and the rest black. Have been doing it for quite a white without any issue on the MK3S+. The issues in the pictures are on the first layer (0.2mm) so it does not depend on the color change

RE: First layer discoloration

Can you try printing that part with white and another dark but not black color (red/blue perhaps)?

Since it sounds like you end one part with black then start the next print with white, I’m still wondering if this is some filament residue in the nozzle. You end the print with black, unload black and load white, start a new print, perimeters print first and end up grey until all of the black residue has been purged by the white filament.

At this point, even printing the part in all white would point to this being the issue. Print the same file but unload and reload white at the color change. If the second print begins perfectly white, that should be enough to prove this residue theory. 

RE: First layer discoloration

The first 5 layers are white (1 mm), the rest is bleack. The issue is on the first layer, so this is not the case of filament stuck in the extruder

RE:

What I am trying to get at is you indicate you have been doing this for "quite a while." You are either referring to this type of model with a similar transition or this exact model with this exact transition. Either way, if you are repeatedly printing white layers followed by black layers, then when one print ends and the next starts, you are transitioning from black to white.

If you open your slicer and walk through the tool path of the first layer, I am willing to bet you will see it print the letter perimeters first, followed by the innermost external perimeter, ending on the very outside perimeter. I have attached a photo of a black-then-white print of my own where you can see the exact same thing happening. It starts in the bottom middle and follows the perimeter left then up until it fades to total white. In my case, it was on the same layer but your case is no different--you printed with black and the next thing printed was white.

If you at least try my test(s) from above, we could completely eliminate this as a possible issue and start troubleshooting other things.

RE: First layer discoloration

Justin I see your point, however also when the previous print ends with a white color and I start a new one with a white color I have the same issue (I tried already). On my MK3S I have never had this problem and I have been printing same parts with same colors for few years already. Must be something else