One of the purple science materials requires five ingredients, one of which is petro gas, therefore must be crafted at a mk3 assy machine.

Mk3 assy machines require purple science though, as mk2 machines can only handle four ingredients?

This seems unintended, so I thought I'd bring it to your attention.

Using .16.3, but I checked .16.11 to see if it had been fixed already and it appears not.
Couple screenshots for reference, ignore the massive numbers.
https://cdn.discordapp.com/attachments/380176464546365453/440995007529222144/unknown.png
https://cdn.discordapp.com/attachments/380176464546365453/440995203680305163/unknown.png

biosilicate extract is made in chemical plant, not in assembler
it's 1 fluid (petroleum), and 4 items, there is no issue with tech required.
also no issue with "feeding", because you need 1 pipe and 2 belts as input.

I see! Would be nice if the tooltips in the tech trees indicated what machines the components are made in, wouldn't it?

Thank you for the response, that helps my motivation return!

FYI even blue assembler can craft 5 item recipe, if it's 4 solids, 1 liquid, blue assembler has 4 inserter slots and 1 pipe input.