Regarding this artfact:

Artifact "Efficient Crafters" - 2% reduction

Crafter ingredients reduced by 2%

Passive

When crafting a Struct, it requires 410 Lead bars without the artifact, and 402 with the artifact = 1.9% reduction, this is expected.

When crafting Glass, it requires 9 Silver bars without the artifact but only 8 with the artifact. This is actually an 11% reduction, but no complaints.

But when crafting a Boiling Flask, it requires 19 Gold bars both with or without the artifact. Reduction to 18 would be a 5.2% reduction so not surprised that it doesn't reduce.

Anyone else seen this? Or able to explain the variation?

Sounds like the Struct and Boiling Flask are correct, but the Glass is wrong. Can you double-check that the Glass actually goes from 9 to 8 with only a 2% reduction? I don't see how that's possible.

I think the actual ingredient costs for the recipes do have decimals in the prices, but you can't see them because Fizzer set the lowest significant figure shown to the ones digit. The values shown use standard rounding, so the actual price probably went from 8.6 silver bars to 8.428 (8.6-2%), which would cause the displayed value to change since that crosses a .5, but with the boiling flask, the actual number of gold bars needed probably went from 19.2 to 18.816 (19.2-2%), which doesn't cross a .5 and thus the displayed value wouldn't change.

Here are some screenshots. Agree that Struct & Boiling Flask align with 1.5%, and Glass is the outlier.

Without the artifact:


With the artifact:


On a separate point, I know a recent update made it to the quantity of items required for recipes was increased so in cases like this that some % reduction doesn't round down to 0 benefit. But doesn't seem like it's enough, b/c it only gives benefit (ignoring the erroneous Glass example here) for the items with non-valuable ingredients. It's for those valuable ingredients where it is most desirable and unfortunate if it actually yields no benefit on those. Would be awfully nice if perhaps the minimum benefit was "1 item". (;

I've seen some cases where "0.5 items" were awarded - maybe if was in resource caches. And I know I definitely received 1.05 lanthanum bars from a resource cache previously - not sure what this actually results to, or if it just rounded down to 1 in my inventory. But these "partial items" might be an answer to allowing the % based artifacts to still add some value.

and also a problem with "ore sell values" card which doesnt change the price of ceramics and Boiling Flask ...

would need to check the other alloys and also all my cards .
Because what's the point of getting them if they dont work.
I might be kinda rude but when i spend money, i want to get something, dont you.

but love and peave to everyone here, my friends

I noticed that crafter ingredients don't round down. If you research the "10% crafter ingredients reduction" tech, only recipes with 10+ ingredients of one type see the reduction.
Let's say you have a recipe requiring 9 bars. With the -10% tech, you'll need 8.1 bars, rounded up to 9. With the additional 2%, you'll need 7.92 bars, rounded up to 8.
For a recipe requiring 21 bars, the -10% tech reduces it to 18.9 (rounded to 19), the extra 2% reduces it to 18.48 (rounded to the same 19).
I assume the 410 -> 402 reduction was before researching the -10% tech. 2% reduction means a cost of 401.8 bars, rounded to 402. With the tech, cost is 369 bars, and with both tech and artifact, 360.8 rounded to 361.
Same in the example above, if the recipe costs 19 bars without the tech, cost is 18.62 with the 2% reduction (still 19); 17.1 with just the tech (rounded to 18); and 16.72 with both (rounded to 17).

The 2% artifact by itself is rarely useful, but combined with the 10% tech you might see a significant change. When scheduling your crafter to work on a new recipe, check if the artifact reduces the required ingredients. If not, use another artifact that gives some other benefit.

and also a problem with "ore sell values" card which doesnt change the price of ceramics and Boiling Flask ...

Ceramics and Boiling Flasks aren't ores. You'll know if a resource is an ore since it ends with Ore, such as Copper Ore, Gold Ore, etc.

Let's say you have a recipe requiring 9 bars. With the -10% tech, you'll need 8.1 bars, rounded up to 9. With the additional 2%, you'll need 7.92 bars, rounded up to 8.
For a recipe requiring 21 bars, the -10% tech reduces it to 18.9 (rounded to 19), the extra 2% reduces it to 18.48 (rounded to the same 19).

Came here to write this -- you are correct, this is the actual answer.