[Amanita]

Hi, I'm new to this forum, and I'm hoping someone can help me with a question about testing for silk fibres.

I want to test some silk which I bought in Thailand, as well as an unknown fabric lining a piece of furniture that I was given.

I found these instructions: "At room temperature, mix a solution of 16 g copper sulfate (CuSO4) in 150 cc of water. Then add 8-10 g glycerine. Now mix in caustic soda (sodium hydroxide: NaOH) until the solution becomes clear. A small sample of natural silk will completely dissolve but this mixture won't affect cotton, rayon, and nylon."

I studied chemistry in school, but it's a long time since I've done any formally.  Perhaps unwisely, I tried following the instructions to see if I could get it to work, but I just ended up with a thick, murky turquoise mess.

I tried searching for instructions or videos of this same process, but I couldn't find anything outside of silk-buying websites.  It seems to be related to a process for making Copper Hydroxide, but I don't understand the purpose of the glycerine.  It also seems similar to the Biuret test, but that calls for Potassium sodium tartrate instead of glycerine, and it requires the protein to be in an aqueous sample.

My questions are:

• Do the above instructions sound plausible for testing for silk?
• If so, what errors am I likely to have made to lead to this outcome?
• If not, is there any test which I could do with fairly minimal equipment which would let me test whether a fabric is made of silk?

Thanks in advance for any insight.

[billnotgatez]

Is there a link we can use for your instructions

I found these instructions

[Amanita]

Here are a couple of sites:
http://www.hand-dyedfibers.com/oscnuked/modules.php?name=News&file=article&sid=7
http://www.enjoysilk.com/blog/how-to-identify-natural-silk
As you can see, there is not really any more context for the test.  I haven't been able to find any reference to it outside of this type of site.

[billnotgatez]

I believe you also mention Biuret test

http://en.wikipedia.org/wiki/Biuret_test

Also a link of interest would be the WIKI on silk

http://en.wikipedia.org/wiki/Silk
http://en.wikipedia.org/wiki/Protein

some other WIKI links are
http://en.wikipedia.org/wiki/Cotton
http://en.wikipedia.org/wiki/Rayon
http://en.wikipedia.org/wiki/Nylon

[billnotgatez]

Given that I have never done this test --

The sources that you posted of the recipe' for the formulation of the
copper sulfate (CuSO4) + water + glycerine + caustic soda (sodium hydroxide: NaOH)
solution says it turns clear.

What is not said is whether it is a clear blue/green or if it is clear like water.
I would assume it is that the caustic soda causes it to change from a cloudy blue/green to a transparent blue/green.
I am also guessing that the glycerine is present to lend to the solvent properties.

Do you get the 

a thick, murky turquoise mess

before or after you introduce the fabric to be tested?

[Amanita]

 Thanks for adding the extra links, sorry, it didn't occur to me that everyone was not familiar with the difference between the fibres!

I would assume it is that the caustic soda causes it to change from a cloudy blue/green to a transparent blue/green.

That's the funny thing, it started out as a perfectly clear blue solution, and the glycerine didn't cause any visible change, but adding the caustic soda caused a lot of deep blue particles to appear, and the background colour of the liquid was pale green.  I stirred it quite a bit, but the particles just broke up and stayed in suspension.

I was wondering if the addition of the glycerine was meant to make a solution which these particles would dissolve in, would that make sense?

Given that it never became clear, I figured I had just messed it up and didn't try adding the silk.  If I just dropped it in I wouldn't have been able to see it, and I didn't want to risk my tweezers since I didn't know what I had ended up with...

(edited because I accidentally posted before I was finished.)

[Amanita]

Just to add some further detail, in case it's not clear to those reading; the idea is to produce a liquid which will dissolve protein-based fibres (such as silk), but not collagen-based fibres (such as cotton) or synthetics (such as acrylic).

[Arkcon]

but not collagen-based fibres (such as cotton)

Cotton is cellulose based.  Collagen, although not really a protein, would like behave as one for simple chemical tests.  Short of a digestive enzyme cocktail, or boiling HCl, it would be difficult to completely dissolve a protein sample, particularly a fabric sample, which is more or less designed to survive the elements while the caterpillar pupates.  In fact fabric fibers made of protein -- either silk or wool, are quite resilient to enzymatic and chemical attack.  These are solid precipitated proteins and very durable, as distinct from say, meat.

Your original recipe may well dissolve a few isolated threads of silk, but not a bulk sample.  The funny thing is, cellulose, especially cotton, will definitely dissolve in strong caustic solution, that's how Rayon is made.  So while your reference may be working fine, it doesn't make much sense chemically.,

[Amanita]

Thanks for the reply Arkcon.

(I did mean cellulose, sorry, no idea where 'collagen' came from there!)

So, it sounds like this is a wild goose chase then?  I wonder if these pages are all pulling from the same original source which got it backwards.  From what you're saying, it would be easier to dissolve the potential non-silk alternatives.  Do you think there's a way I could set up a test based on that concept?  I dont mind too much how it's achieved, I'd mostly like to be sure that this fabric is genuine silk before I spend a lot of time working with it.  The described test sounded like a foolproof way of being sure, so I'm disappointed if it's just gibberish.

[Arkcon]

Historically speaking, identifying fabric fibers is trivial.  They are very distinctive microscopically.  See: here:  http://www.microlabgallery.com/ClothingFiberFile.aspx

[Arkcon]

And some other fabric fiber tests:

http://www.sewanee.edu/chem/Chem&Art/Detail_Pages/Projects_2007/Garfield/index.htm

https://www.cci-icc.gc.ca/publications/notes/13-18-eng.aspx

[Amanita]

Thanks again, I'll have a read through these in detail and see if I can get some more ideas.  The burn testing so far has been inconclusive, possibly indicating a fibre blend or a coating of some type.  I don't have access to a microscope (which is an option I hadn't looked at, and might investigate further), but I do have a selection of dyes, which might definitely help.