Just as an aside, I've been experimenting to get the effect of gratings as follows.
1. Roll out plasticene so it's flat.
2. 'Scrape' parallel lines/grooves using suitable scale saw blade (normal hacksaw is about 1:96). It helps to have a straight edge along one side.
3. Repeat scraping at 90 degrees. You should then have sort of dimples in a grid pattern which is the 'negative' of the grating.
4. Add plasticene wall around.
5. Spray with a little plumbing silicone spray.
6. Pour in resin to whatever thickness you need plus a bit for fettling.
7. When set, remove and clean up and you should have a 'budget' grating. No holes right through, of course.
8. Clean off any excess plasticene/silicone with a nail brush and washing up liquid.
9. Wash over with well diluted acrylic paint, probably several times. The paint collects in the 'holes' giving an appropriate contrast. As a final wash you can use black or very dark brown to accentuate the shading.
Works for me but..............
Tony
First Pic is after first wash of paint. Second is the finished article.