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Cochineal lake failure


Jeremy Osner
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My first experiment of making cochineal lake appears to have failed; 5 days after making the dye and adding alum and alkali, I can see no separation of the pigment (although the dye has thickened a bit). Apparently my idea that I could just divide the ingredient quantities in a recipe I found for carmine lake (in "Manufacture of mineral and lake pigments" by Joseph Bersch) was incorrect.

I made 2.5 liters of red dye using 40g ground cochineal and 2.4g cream of tartar, boiling for 15 minutes. I then strained the dye into glass jars, leaving them half empty, and added a solution of alum made with 4g alum and a cup of water, divided evenly among the jars. I made a solution of soda ash using 1 Tbsp ash and 1/2 cup water, and started adding it to the jars with an eye-dropper, expecting it to foam up; I saw no foam at all. I added more of the alkali solution til I had used the full 1/2c, still nothing. I got a bit panicked, and thought maybe the issue was that there was not enough alum; so I made more alum solution (with about 8g alum) and poured that in, and made more alkali solution and added that. Saw a little bit of foaming but nothing like on the videos I'd been watching of lake making. I noticed that the dye in the jars looked a bit thicker than it had initially, so I thought maybe it was starting to precipitate. Left it alone thinking, better to just wait and see -- that was Friday.

Any clues what my mistake was? A friend (who has also never made lake pigment) is planning to try making madder lake, hopefully I can at least give him some pointers about what not to do. Does temperature play any role? The jars are sitting in the garage where it is very cold, though I don't think it was below freezing.

I guess I will try filtering what is in the jars and see if there is anything solid in them that I can dry and make paint out of...

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If you are going to get a precipitate, it happens instantly... waiting won't do much good.  

I can't troubleshoot your process, as I have never tried that particular recipe, but 40g of cochineal seems like a huge amount to use up for a process you are not sure will work, and seems to me out of proportion to the much smaller mass of alum.  But again, I don't know this recipe.

In the Jan 2016 issue of The Strad (trade secrets), there is a much simpler method of making and coloring lake.  I have tried it, and it seems to work... although cochineal still tends to come out purple-ish unless adjusted with some yellow.

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I think that the proportion between cochineal and alum should be 1:1 (i.e. 10g alum and 10g cochineal), then adding the alkaline solution little by little until precipitation occurs. The solutions should be allowed to stand (for an hour or more) before proceeding to the next step.

Regarding the temperature, I have no direct experience with cochineal, but in the case of madder the lower the temperature (ambient) the purer and lighter the red, the higher the temperature (boiling) the darker and brownish the red will be, with a visible difference every 10°/15° C difference.

If you are a chemist, making a stoichiometric calculation of the quantities would be ideal to obtain the maximum color intensity, but if you are not able (I am not) to err a bit by abounding with chemicals it is more prudent as if an excess remains you can eliminate it with the final washes of the precipitated lake before drying it, even if it will require much more time and liters of distilled water

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@ Jeremy - While it is not essential, I have found it helpful to have some means of measuring pH, either a pH meter or pH 0-14 indicator strips.  This gives at least some indication of where you are starting from and where you are when attempting to create the precipitate (approximately pH 7).

There are many variables that will impact on what you end up producing, e.g., acid versus alkali extraction, whether you are using a first or subsequent extraction, molar strengths of the acid and alkali components, purity of water used, the speed at which the precipitate is formed, how vigorously the brew is being agitated at the point that the precipitate is being formed, temperatures employed at various points throughout the process, etc., etc., etc.. 

If I was you I would start out by making separate alum and soda ash solutions, maybe 250ml 0.3 molar of each in glass beakers or clear glass jars.  Warm the soda ash solution to maybe 60 deg.C..  Drop a number of cochineal beetles (don't bother grinding them) into the warmed soda ash solution until you see very good colour developing.  Once deep colour has developed, allow to cool to 40 deg. C. or less.  Remove cochineal beetles via filtering or use of a fine stainless steel sieve.  Very slowly add the alum solution to the coloured soda ash solution, stirring the soda ash solution as you do so.  (Use a glass stirring rod if you have one available.)  At the point that you see froth beginning to appear, take a drop of the solution on the end of your stirring rod and dab the drop on to a piece of filter paper.  Initially all you will see is a weakly coloured smudge on the paper.  Keep adding the alum solution and keep testing drops on the filter paper.  At a certain point you should notice a very obvious strongly coloured solid ring forming on the paper.  Stop there and allow everything to settle.  The coloured pigment/precipitate should gradually settle in the bottom of the beaker/jar with a clear but likely quite strongly coloured solution sitting above that.  Very carefully pour off as much of the clear solution as you can without losing any of the precipitate.  Add fresh water to the pigment/precipitate and agitate with a stirring rod.  Allow the precipitate to settle and again pour off the clear solution above this.  Repeat this process until the clear solution has no colour associated with it.  Pour off as much of the clear colourless solution as you can, agitate what remains and filter this etc..  

Note this is a very basic and small scale off the top of my head suggestion but will at least get you started, giving you a practical understanding of the process involved.  If this doesn't work, I would suggest that there might be some issue with your soda ash or alum.

@ Don - In creating your initial cochineal dye bath, it might be worth considering throwing out what forms in the first minute or so.  Remaking the dye bath with the same partially used cochineal can sometimes result in a reduced bluish aspect.  Also it may be worth experimenting with various acid versus alkali extractions and various molar strengths.  Also the temperatures of the solutions during precipitation can affect colour outcomes etc., etc...

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The original poster went wrong by adding soda ash , it is not required for the recipe in the Bersch book.

(You dont add soda ash or potassium carbonate.)

Also making the pigment carmine is slightly different than the usual lake process. Its made under acidic conditions if you want red coloured pigment.

Ive done the Bersch book method years ago with some success, potassium oxalate is better than the cream of tartar and if i recall the cochineal was extracted with water and potassium nitrate or very dilute sulphuric acid.

Every thing must be done with non iron/ steel  utensils

It is also a lengthy process if you follow the Bersch book method.

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OP doesn't say how much water was involved. Making madder lake I found that if there was too little water--too concentrated of the solutions involved--nothing would happen. If everything is right, as you pour in the second solution the precipitate will form instantly where the two meet. If that doesn't happen, something is wrong. I found that adding more water at that point worked. You can't really have too much water.

No guarantee, but that's my experience.

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Way to go, John Harte! Good information generously and kindly given. 

To the OP - make sure you're using fresh reagents, too. You can also push the color around with your choice of metal salt - zinc or tin instead of alum, as an example. You can also make a precipitant with a blend of salts to further influence the color. E.g. a combination of zinc and tin in Madder will give oranges.

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On 2/17/2022 at 4:33 PM, John Harte said:

@ Jeremy - While it is not essential, I have found it helpful to have some means of measuring pH, either a pH meter or pH 0-14 indicator strips.  This gives at least some indication of where you are starting from and where you are when attempting to create the precipitate (approximately pH 7).

There are many variables that will impact on what you end up producing, e.g., acid versus alkali extraction, whether you are using a first or subsequent extraction, molar strengths of the acid and alkali components, purity of water used, the speed at which the precipitate is formed, how vigorously the brew is being agitated at the point that the precipitate is being formed, temperatures employed at various points throughout the process, etc., etc., etc.. 

If I was you I would start out by making separate alum and soda ash solutions, maybe 250ml 0.3 molar of each in glass beakers or clear glass jars.  Warm the soda ash solution to maybe 60 deg.C..  Drop a number of cochineal beetles (don't bother grinding them) into the warmed soda ash solution until you see very good colour developing.  Once deep colour has developed, allow to cool to 40 deg. C. or less.  Remove cochineal beetles via filtering or use of a fine stainless steel sieve.  Very slowly add the alum solution to the coloured soda ash solution, stirring the soda ash solution as you do so.  (Use a glass stirring rod if you have one available.)  At the point that you see froth beginning to appear, take a drop of the solution on the end of your stirring rod and dab the drop on to a piece of filter paper.  Initially all you will see is a weakly coloured smudge on the paper.  Keep adding the alum solution and keep testing drops on the filter paper.  At a certain point you should notice a very obvious strongly coloured solid ring forming on the paper.  Stop there and allow everything to settle.  The coloured pigment/precipitate should gradually settle in the bottom of the beaker/jar with a clear but likely quite strongly coloured solution sitting above that.  Very carefully pour off as much of the clear solution as you can without losing any of the precipitate.  Add fresh water to the pigment/precipitate and agitate with a stirring rod.  Allow the precipitate to settle and again pour off the clear solution above this.  Repeat this process until the clear solution has no colour associated with it.  Pour off as much of the clear colourless solution as you can, agitate what remains and filter this etc..  

Note this is a very basic and small scale off the top of my head suggestion but will at least get you started, giving you a practical understanding of the process involved.  If this doesn't work, I would suggest that there might be some issue with your soda ash or alum.

@ Don - In creating your initial cochineal dye bath, it might be worth considering throwing out what forms in the first minute or so.  Remaking the dye bath with the same partially used cochineal can sometimes result in a reduced bluish aspect.  Also it may be worth experimenting with various acid versus alkali extractions and various molar strengths.  Also the temperatures of the solutions during precipitation can affect colour outcomes etc., etc...

Thanks John....well said

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