You Are Viewing The Forums As A Guest

Welcome to Cooking The Books.
Please have a look around and enjoy the various threads available to you as a guest here.
For full access to the boards you will need to register to join.
Details are in the Welcome board and you can access the registration page via the button below.




If you are having problems with registration then contact forum@tudorcook.co.uk

How thin is gold leaf?

Comments and chat about the cookery events at Hampton Court Palace or any other history cooking, methods, techniques, events, kitchens or things not strictly recipe related.

How thin is gold leaf?

Postby kitchen clerk » Tue Jan 22, 2013 8:56 pm

So, how thick is gold leaf?

Very thin, obviously, but it is surprisingly difficult to find out exactly. So how about going back to basics and working it out. The place to start is with the manufactures and distributors, who have an interest in being precise about such a delicate and valuable material. Gold leaf is sold in books of 25 sheets, and usually each sheet is 3 3/8 inches square. The manufactures, quite sensibly, use the weight of the gold to define the quality of their product. The standard being how much gold for a thousand sheets.

For example the German Monarch company produces a book of pure gold leaf, 24kt, and 19 grams per 1000 leaves. Pure gold leaf isn't as common as you might think, Monarch make another twenty varieties of gold leaf, from 23 3/4kt, to 9kt. Alloying with copper makes the leaf a darker and redder colour, and with silver, whiter. The Monarch range has descriptive names; Rosenoble, Red Gold, French Pale, Moon Gold, Lemon. And Edible Gold; owing to possible amounts of copper, not all gold leaf is food safe.

So a thousand leaves of 3 3/8... each leaf is 85.725mm each side and has an area of 7348.7 square millimetres, so a thousand of them gives an area of 7,348,775 square millimetres. Next to find the volume of this large thin sheet of gold, we know the weight of it, 19 grams, and as the density of gold is 19.32 grams per cubic centimetre, (or 0.01932 grams per cubic millimetre) our volume is 983.4 cubic millimetres. As volume is area times thickness, division by the area gives the thickness of the gold leaf as, 0.000134 mm. This is more usually expressed in microns, which are a thousandth of a millimetre.

So the thickness of this variety of gold leaf is 0.134 microns. Which is very thin, too thin to see. Literally. It is thinner than the wavelength of light.

Monarch makes gold leaf in many weights, but lets turn to the long established French brand Dauvet and one of it's coloured gold leaves, 'Rouge', it's 23kt, which means that one part in 24 isn't gold, certainly copper in this case. And 14 grams per thousand sheets, but that's just the gold, so the total weight is 14.6 grams. This time it's the French metric standard of 84 mm square, so the total area is 7,056,000 square millimetres. Having one twenty-fourth copper drops the density to 18.88, so volume is 773 cubic millimetres. Divided by area gives 0.1096 microns.
To reach the thickness of a millimetre, 9,123 sheets would have laid on top of each other.

That was the easy bit, now to work out how many atoms thick it is. Imagine we have a leaf of the pure gold, the 0.134 micron one, and we manage to cut a tiny cube, with sides the thickness of the leaf. This is impossible of course, as the cube would be the size of a virus. And the volume of this tiny cube; 2.39 times ten to the power of minus twelve, which is another way of saying there are twelve zeros between the decimal point and the 2.39. So a small number then. Multiply by the density to find out that our tiny cube weighs 4.63 times ten to the power of minus fourteen grams.

Time for a bit of chemistry, back in the day chemists worked out that a certain amount of a substance would react with another amount of another substance. For example to make gold iodide, AuI, you could combine 196.967 grams of gold with 126.904 grams of iodine. They soon worked out (two hundred years ago) that these two amounts contained the same number of atoms, they are now called the atomic weights of these elements. And a lot later the actual number of atoms in these quantities was determined, and it is 6.022 times ten to the power of 23. Yes it's a number that has 23 zeros... The amount of a substance that has that amount of atoms is called a mole, we need to work how many moles are in are tiny cube, so divide the weight of our cube by the atomic weight of gold, 196.967, which is 2.35 times ten to the power of minus 16. We know how many atoms are in a mole, so now it's time to multiply an enormously big number by a ridiculously small number.

141,565,233, the number of atoms in that tiny cube, more or less. The atoms in gold are arraigned in a cubic structure, which is handy for us, because what we need to do now is to find the cube root of the above number to find the number of atoms on each side of the cube, which is how many atoms thick our gold leaf is.

521. That's it. That many atoms. The same calculation done on the thinner French gold leaf gives the result of 427 atoms. And it's hard to imagine how small an atom is; and to imagine that piece of gold leaf on your finger is only a few hundred atoms thick.

There is another way to find the number of atoms, slightly less satisfying though as it involves looking up the size of gold atoms and dividing into the thickness of the leaf. Atoms are fuzzy things, and there seem to be many definitions of their size. 'Empirically measured radii', sounds as good as any, the figure being 135 pm. That's picometres, which are of course, very, very small, a millionth of a micron in fact. Multiply by two to get the diameter of the atom, 270 pm.

The 19 gram gold leaf, 133,823 pm thick, divided by 270 pm; 495.6 atoms.
And the 14 gram one; 406 atoms.
Amazed how close these figures are to the calculated ones above.
Last edited by kitchen clerk on Mon Jan 28, 2013 8:41 am, edited 2 times in total.

For this message the author kitchen clerk has received thanks:
tudorcook
kitchen clerk
Fancy-Fancy
Fancy-Fancy
 
Posts: 129
Joined: Fri Aug 20, 2010 11:36 pm
Has thanked: 8 times
Have thanks: 11 times

Re: How thin is gold leaf?

Postby Bassoonbloke » Wed Jan 23, 2013 10:09 am

Hi Robert,

What an interesting problem and a nice write up as to how you worked it out !!
At the end of the day what we can say is :- "It's Bloody Thin !!" :shock:
This is why gold leaf can be eaten (within reason) and it causes no problems (it's also quite non reactive).
Having been a senior science tech for about 12 years (although i'm now working with computers and networks), I have a general interest in anything like this (my fields being Physics and Chemistry & a bit of Biology).
Hope you're not too snowed in where you are.

See you at the Palace in Feb,
Cheers,
Alan. :thumbup:
User avatar
Bassoonbloke
Talkative
Talkative
 
Posts: 151
Joined: Mon Dec 05, 2011 11:12 am
Location: South East London.
Has thanked: 0 time
Have thanks: 3 times

Re: How thin is gold leaf?

Postby Bassoonbloke » Wed Jan 23, 2013 10:10 am

Hi Robert,

What an interesting problem and a nice write up as to how you worked it out !!
At the end of the day what we can say is :- "It's Bloody Thin !!" :shock:
This is why gold leaf can be eaten (within reason) and it causes no problems (it's also quite non reactive).
Having been a senior science tech for about 12 years (although i'm now working with computers and networks), I have a general interest in anything like this (my fields being Physics and Chemistry & a bit of Biology).
Hope you're not too snowed in where you are.

See you at the Palace in Feb,
Cheers,
Alan. :thumbup:
User avatar
Bassoonbloke
Talkative
Talkative
 
Posts: 151
Joined: Mon Dec 05, 2011 11:12 am
Location: South East London.
Has thanked: 0 time
Have thanks: 3 times

Re: How thin is gold leaf?

Postby Bassoonbloke » Wed Jan 23, 2013 10:11 am

OK it was so good my computer decided to post an answer twice !! :dizzy:

Alan.
User avatar
Bassoonbloke
Talkative
Talkative
 
Posts: 151
Joined: Mon Dec 05, 2011 11:12 am
Location: South East London.
Has thanked: 0 time
Have thanks: 3 times

Re: How thin is gold leaf?

Postby TerryL » Wed Jan 23, 2013 11:56 am

Nice one Robert / Kitchen Clerk - it's good to see some "articles" on here.

Now, about those write ups on some of the recipes you've experimented with...
Terry says... All comments in my messages are entirely my own opinion, and no other idiots.
User avatar
TerryL
Rambler
Rambler
 
Posts: 1244
Joined: Sat Aug 21, 2010 10:04 pm
Location: London, UK
Has thanked: 15 times
Have thanks: 50 times

Re: How thin is gold leaf?

Postby Bassoonbloke » Wed Jan 23, 2013 12:01 pm

Crikey!!

He's not doing cooking as well is he :-o

Alan.
User avatar
Bassoonbloke
Talkative
Talkative
 
Posts: 151
Joined: Mon Dec 05, 2011 11:12 am
Location: South East London.
Has thanked: 0 time
Have thanks: 3 times

Re: How thin is gold leaf?

Postby TerryL » Wed Jan 23, 2013 12:38 pm

Bassoonbloke wrote:Crikey!!

He's not doing cooking as well is he :-o

Alan.


Oh yes, they let him loose actually cooking and he does it his way - trying variations on the recipes (which are a bit vague at times) and tries to find what works best, and often asking the visitors to... it's an interesting approach and some of the younger visitors really enjoy being able to get a bit interactive, even if the spice mixes aren't always quite what most would expect.

I quite liked the cover tarts - especially the scrambled egg variant, but then I like scrambled eggs as much as I like custard :-D
Terry says... All comments in my messages are entirely my own opinion, and no other idiots.
User avatar
TerryL
Rambler
Rambler
 
Posts: 1244
Joined: Sat Aug 21, 2010 10:04 pm
Location: London, UK
Has thanked: 15 times
Have thanks: 50 times

Re: How thin is gold leaf?

Postby kitchen clerk » Wed Jan 23, 2013 7:20 pm

Made a mistake!
The karat system of purity uses proportions of mass, so the mass of gold divided by the total mass multiplied by 24 equals the karat value.
So an amount of 23 karat gold, that contains 14 grams of gold, will always weight 14.608 grams, no matter what it is alloyed with.
Edited it to take that into account, which makes the French gold leaf a bit thicker, of should I say, less thinner!
Thanks Alan, as you can see, it could do with a bit of peer review...
kitchen clerk
Fancy-Fancy
Fancy-Fancy
 
Posts: 129
Joined: Fri Aug 20, 2010 11:36 pm
Has thanked: 8 times
Have thanks: 11 times

Re: How thin is gold leaf?

Postby TerryL » Wed Jan 23, 2013 8:54 pm

A peer review requires peers - and they are few and far between. At the end of the day it still comes down to gold leaf being extremely thin, making even a roll-your-own cigarette paper look like a 2 inch plank (that's approx 51mm for those of a metric persuasion).

I also wonder about the number of gold atoms thick, I'm wondering if the figures for the diameter of an atom, are all there is, and thus the atoms are in "physical" contact, or if there is an additional spacing (electrostatic forces from the "electron clouds" of adjacent atoms). Also, whether the leaf is looked at as a single metallic crystal, or if a cluster of crystals, with perhaps inter-crystal spacings.

I wonder if you could pop along to NPL (National Physical Laboratory) one day and ask someone there - it's not far from the palace. I know the R68 bus I catch stops outside there, and it's where they change drivers sometimes, but I'd probably forget to get off and ask, and I'm not sure there'd be anyone to ask on a weekend when I'm on the bus.
Terry says... All comments in my messages are entirely my own opinion, and no other idiots.
User avatar
TerryL
Rambler
Rambler
 
Posts: 1244
Joined: Sat Aug 21, 2010 10:04 pm
Location: London, UK
Has thanked: 15 times
Have thanks: 50 times

Re: How thin is gold leaf?

Postby kitchen clerk » Thu Jan 24, 2013 12:13 am

There of lots of values for the atomic radius of gold!
It was the bit of the essay I wasn't comfortable with, as I had to look up the values online, without really understanding what the difference between them is. The values are between 121 pm and 174 pm, and had I been a bit dishonest I could have chosen the one that fitted the calculations closest...
I have just worked out what this figure is, and am very surprised that, for both types of gold leaf, the number is the same, 128 pm.
This is very strange, does this mean I now have my own value for the atomic radius of gold?
kitchen clerk
Fancy-Fancy
Fancy-Fancy
 
Posts: 129
Joined: Fri Aug 20, 2010 11:36 pm
Has thanked: 8 times
Have thanks: 11 times

Next

Return to History Cooking & Kitchens

Who is online

Users browsing this forum: No registered users and 0 guests

cron