I’m printing flat shells and I noticed the same effect. The effect is very well visible for horizontal areas which are facing to the raft and have supports. My understanding (proved by different experiments) is that when you dip the detail into the resin and then you take it out the resin can’t flow away quickly from areas near horizontal and stays there much longer. Rafts make things worse as the cappliliar effects caused by thin supports hold the resin.
When there is trapped resin which can’t flow out quickly and when the detail printing takes long time the parasitic resin curing can solidify the resin. During the exposure there is inevitable parasitic light which diffuses through the object and sensibilizes or semi-cures any residual resin. All print details in this area will me “smeared” and covered by semi-cured resin and this is what looks like bad quality print.
I tried different ways to clean the semi-cured resin but in vain - it’s obviously softer than the other resin but it’s cured enough to be dissolvable.
The solution (patch) is to orient the details in such way that the areas close to horizontal with supports are not critical or rotate the detail to avoid horizontal areas with supports (resin is drained quickly from the area).
If the detail orientation/structure create small areas and “vanes” where liquid resin can be trapped the quality in this places will be compromised, supports in these areas make things much worse.
Maybe the real solution is the software to detect “vane” conditions just like now it detects “cup” condition where area is sealed. Once the user is aware for this condition he can do some things:
- Rotate the detail to avoid near horizontal areas
- Prevent resin “vanes” and add drainage holes if needed
- Decrease number of supports in the area
In short - changing the orientation to avoid horizontal areas, decreasing number of supports in the area and adding some drainage holes can completely remove the effect.