
An 18-carat gold nugget made of plastic - Lagogarda
https://ethz.ch/en/news-and-events/eth-news/news/2020/01/gold-nugget-made-of-plastic.html
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virtualritz
I'm a bit puzzled that this is news.

The technique of using metal or stone powder with resins to create fake metal
or stones is used since years.

When I was living in HK, in Sham Shui Po, I always wondered why there were
these street stalls selling huge blocks of jade for cheap. Later a local
friend told me it was just blocks of resin with embedded jade powder and other
stuff. E.g. other stones ground up to simulate imperfections and dyes for the
resin.

When used with metal powders to create sculptures, jewelry, etc. the technique
is called 'cold casting'.

See e.g.
[https://www.youtube.com/watch?v=7VBVU3FNt-s](https://www.youtube.com/watch?v=7VBVU3FNt-s)

Ofc., people do this with gold too:
[https://www.reddit.com/r/ResinCasting/comments/bfiixq/cold_c...](https://www.reddit.com/r/ResinCasting/comments/bfiixq/cold_cast_gold_dice_set_with_bonus_skull/)

The problem with all this is that these materials have plastic-like
properties. The article mentions the sound the fake gold nugget make when
hitting a surface sounding like plastic. This is one of the issues.

The weight is another one. Surface feel/texture depends on various factors.

The bottom line is: these materials look like the real thing but they don't
feel/sound/behave like it.

~~~
beatgammit
It's 18k gold that weighs less than most 18k gold. So, if you want the look of
18k gold without the weight, this is one way of getting it.

I don't know how novel it is, but that sounds like an interesting material for
people who don't like current high end jewelry due to the weight, but still
want the aesthetics.

------
lowdose
> No one wants to wear a heavy watch on their wrist, even if it’s made of real
> gold. After a time, it becomes uncomfortable and annoying.

This is a huge assumption. Wine tastes better served in a heavier bottle. More
weight objectively does something with value perception.

~~~
BartBoch
Yeah, this caught my attention too. I like my watch to be semi-heavy - I like
to feel it's on my wrist. A huge part of watch-wearing community like heavier
watches.

The author used huge generalization, probably based on his own preferences.

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FlyMoreRockets
A much simpler approach is to alloy gold with titanium. The resulting alloy is
stronger and less dense than pure gold. Carat weight is determined on a weight
fraction and because titanium is low density, a relatively large volume of
titanium can be alloyed with a small volume of gold and still have a high
carat number.

One particular gold-titanium alloy is significantly harder than most steel.

[https://phys.org/news/2016-07-lab-titanium-gold-alloy-
harder...](https://phys.org/news/2016-07-lab-titanium-gold-alloy-harder-
steels.html)

------
dschuler
Apple did something similar with their ceramic/gold composite watch - there's
some good info here:

[https://leancrew.com/all-this/2015/03/apple-gold/](https://leancrew.com/all-
this/2015/03/apple-gold/)

Unsurprisingly, paying a huge premium for a watch with less gold in it wasn't
very appealing to people. Interesting idea though.

------
abrowne
> _Lovers of [...] heavy jewellery will be thrilled._

Presumably not? Lovers of gold jewelry, who _don 't_ like the weight may be,
however.

------
gnicholas
> _The conventional mixture is usually three- quarters gold and one- quarter
> copper, with a density of about 15 g /cm3.

That’s not true for this new lightweight gold: its density is just 1.7 g/cm3.
And nonetheless it is still 18- carat gold._

Imagine comparing jewelry that is all “18 carat”, but some of it has 10x less
actual gold. Seems like there will be a lot of fraud happening during a period
when customers are not yet aware that the minimum amount of gold in an 18
carat piece has been reduced 10x. People will just hear “18 carat” and assume
it means the same thing it meant before.

~~~
burroisolator
I thought 18 carat just means 75% pure gold. If something has 10x less actual
gold does that mean it is 1.8 carats?

~~~
tofof
It has 10x less mass, but is still 75% gold by mass.

It's effectively a gold aerogel that's been solidified to no longer be
gelatinous.

------
tengbretson
What does this enable that wasn't possible with plating or electro forming?

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jotm
It would probably look really nice on a laptop or smartphone. Doesn't sound
cheap to make, though.

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nixpulvis
I'd love to compare hitting both real gold and plastic gold with various kinds
of hard objects.

------
emilfihlman
>radiation shielding

Can someone explain to me what the heck they mean by this?

~~~
dewey
It sounds like it can be used as a radiation shielding material. Similar to
the lead filled vests they use for x-ray scans.

~~~
emilfihlman
Yes but actually no.

~~~
dewey
Can you elaborate or are you just asking questions you know the answer to
already?

~~~
emilfihlman
No, it cannot be used like lead. Radiation shielding of high intensity photons
(X-rays, gamma, ...) works by attenuation. Attenuation is (almost) purely a
function of how much material you have in between and how dense it is.

You can block alpha with anything, beta with any metal surface. I'm wondering
if it's purely just nonsense as I suspect or if there's some aspect I'm not
considering. I mean it does work against beta, so it's useful in that you
don't need an additional surface, but that's pretty stretching.

