Yes, I agree with your argument that even a moderately large air bubble(s) trapped in the stem/lettering will only produce a small error and that this should not be the focus for this analysis (as a side note, one might consider another scenario where higher accuracy is desired, and if there were say 5-10 factors each contributing about 1% error, it may be worthwhile to systematically eliminate each source of error).
amena wrote:Not only taking the purity indicated by the hallmark for good, but also verifying it by X-rays.
X-ray is a great method for determining silver content, but it is inaccessible for many people, and/or the cost may not be justifiable for certain items. As for the mark, it does not indicate purity, and there has been doubt expressed on whether the mark is legitimate. Unfortunately the mark is not being taken for good in this case.
Assuming that the x-ray test is unavailable and the mark cannot be trusted, we need to move down the list of options at our disposal. We are left with: a) specific gravity test, b) acid test, and c) assay.
The specific gravity test is an accessible, non-destructive test that people can use at home, and at the very least, it is accurate enough to differentiate between an item containing a moderate amount of silver and one composed primarily of non-precious metal.
amena wrote:A big enough bubble doesn't make a big difference.
In a similar sense, variations in density due to most
production methods are not large enough to explain away the difference between a measured specific gravity of 8.67 and an expected specific gravity of ~10.0+. Balancing probabilities, this result provides enough evidence to convince me that the spoon has little to no silver content.