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<p>[QUOTE=&quot;Ownedbybear, post: 236719, member: 29&quot;]Highly unlikely to be early plastic with that 19th C pin back. 19th C plastics couldn&#039;t simulate that colour for one thing,&nbsp; and in any it would have degraded and shown signs of that. Many early plastics were unstable in the long term and get stinky and sticky with age orcrack. </p><p><br /></p><p>The lemon juice reaction is with calcium carbonate, not pure calcium. That&#039;s what coral is mainly composed of - CaCo3. Classic acid/base reaction. </p><p><br /></p><p>The milk thing, if ever it works, is down to light refraction rather than alteration of the milk colour. Milk is almost ph neutral so can&#039;t react as such. Bit like the UV on amber test - refraction. </p><p><br /></p><p>Anyone got a spectrometer lying around? </p><p><br /></p><p>Ah. Actually, that&#039;s a thought - if you&#039;ve a diamond tester, see if it shows as glass hardness or if it&#039;s a bit more.[/QUOTE]</p><p><br /></p>

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