Attacking another quadrant of the engraving testpiece with All The Sharpies produced a cheerful mess:
The “300 g” notation is wrong: the innermost scale is on the middle deck, which I engraved with 250 g of downforce, and reads through a window on the top deck. The next scale outward, the inner half of the green block on the left, would be on the upper deck at 300 g, just beyond the innermost scale.
I removed the excess marker with a 320 (-ish) grit abrasive sanding block, producing a remarkable amount of gray dust in the process:
The general idea was to find out what the colors looked like when confined to narrow engraved slots:
It’s enlarged a factor of two from the 600 dpi scanned image by the simple expedient of changing it to 300 dpi, then assuming all the downstream image handling will Do The Right Thing, which could happen.
I sanded it before fully appreciating how even the smallest particle of crud under the styrene sheet ruins the result:
In this section, the scale with green numbers and black ticks was engraved at 300 g and is slightly less abraded than the adjacent scale at 225 g. Guesstimating the depth at 0.13 mm, 0.15 mm at most, the sanding block doesn’t remove much plastic at all … just enough to remove the scales.
The lines are all about 0.1 mm wide and, to the naked eyeball, look about the same as the lines on my K&E Deci-Lon slipstick:, done on a real production line with an actual engraving tool and somebody who knew what he (I’m sure) was doing:
The red CI scale reads right-to-left and, under magnification, you can see where the red ink made its way into the adjacent tick marks. I doubt they were using a pen, but it might be a mechanized roller or dauber.
All in all, sanding works, but it’s messy and poorly controlled.
The Smell of Molten Projects in the Morning 
Maybe scraping?
Spoiler alert: scraping FTW! [grin]
You used to post scaled these pictures scaled down so that when we clicked them we would get big, hi-res versions. I frequently found that very useful, especially when examining detail like you are illustrating, here.
Yes, and WordPress improved the editor so images no longer work that way.
If you other-click on the image and “open in new tab”, then you (should?) get the orignal-size image. Nowhere near as convenient as click-to-open, but that’s WordPress for ya …
As is noted many times on Sarah Hoyt’s blog, (accordingtohoyt dot com) WordPress Delenda Est, or WPDE for short. [grin/wince]
OTOH, you don’t get the random delays before WP deigns to process a post. Seems to be time-of-day or traffic related (not necessarily on the blog being viewed).
I absolutely do not want to sysadmin a site / blog / whatever in addition to tinkering in the Basement Laboratory.
So I’m trapped at a local maximum, where I don’t much like WordPress, but don’t see sufficient benefit in anything else to justify the effort required to change. Bleargh!
Yep, that seems to be the situation for a lot of people. Put up with WP and get Real Work done, or be the sysadmin forever.