# Solder Masks and Pea Soup?



## Astraveller (Mar 3, 2009)

Now we have an AP process that works we have been looking at what else we can strip before we move on to the Clorox process and beyond. You can see from the photo that the plastic sieve (right) contains various bits and pieces being dunked in AP. We discovered that a few of the pc boards we have appear to be gold plated quite well so we decided to have a go at these. The only problem is they are covered in green solder mask.

The first thing we did was to depopulate a couple of boards using hot sand and a good thump. Then we dipped one in caustic soda (left hand dish) – after an hour nothing! I thought it would be a good idea to burn off the green stuff on another bit of gold plated board with a blow torch, which we did. Man that stuff stinks! And is definitely toxic! But it revealed some gold so we put it into the AP to see what would happen.

In the meanwhile I had washed the caustic soda board a few times, to examine it, in clean water (center dish). Also as some of the bits and pieces from the experimental AP dish were being dissolved I rinsed them in the rinse dish (centre). After a short time I noticed that the rinse dish was turning into pea soup. (Homer – “Hmmm, Pea Soup!)

What is this pea soup? A better question might be – How do we get rid of green solder mask?

TIA,

Linton.


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## tamerakshar (Mar 4, 2009)

- you must heat your sodium hydroxide solution to get rid of solder mask, try to jig saw your boards to weaken the green layer and to make it fit into your container which helps you to deal with more boards simultaneously.
- warning:
your sieve looks like metal thing, don't dump it in AP and i recommend not to use it at all.


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## Astraveller (Mar 5, 2009)

Thanks for the input tamerakshar, I thought my post had developed a cloak of invisibility.

The sieve is plastic! I have already figured out that the AP process should only contain copper and gold – what you are seeing is a small test dish that we are using to test what other bits of computers we can use with the AP but thanks for your warning and confirmation.

After posting this thread, I did a bit of digging and found that I should heat the caustic soda but it is a dangerous thing and that there is a solvent that will do it but that it might not financially worth it. (I can’ remember the name or the post, but I have it bookmarked)

Either way, we have enough of these boards to consider trying to give it a go – I guess I was hoping that someone would say “it’s easy, do this and this and this” 

We have a good supply of computers (so we are lucky there!) but are ‘feeling our way’ as how to process them. It took a long time just to get the AP process to work because we only used bleach instead of acid, - duh!

http://goldrefiningforum.com/phpBB3/viewtopic.php?t=4249

Thanks tamerakshar,

Linton,


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## nicknitro (Mar 6, 2009)

Hi all,

Just expanding on this topic a little. Sorry for intrusion, but is it common for boards to contain this much plating under the solder mask? I thought most were copper laminates, until I recently "unconfirmed" found an old accessory board from a PC that appears to have gold wires under the solder mask. The solder mask was very dark-green and where the wires are running it is more blackish. 

Any thoughts Appreciated,
Nick


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## goldsilverpro (Mar 6, 2009)

Unless things have changed, all-gold traces under the mask are not that common. Often, they LOOK like gold but aren't. Looking through the mask, they look like gold. Sometimes, when the mask is removed, they will have a yellowish cast, but this isn't gold. For what purpose would the traces be all-gold plated, anyhow? Before I spent all that time and effort removing the mask, I would absolutely make sure there is gold underneath it.


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## nicknitro (Mar 7, 2009)

Will do Chris, I have a few of the wires soaking in Nitric right now to clean them up a bit, as I kinda pulled/peeled them off the board, and they have some mask / crap attached to them. Once cleaned I will wash and desolve them in AR and test with Stannic. Post results tomorrow night?
As well as source if it is positive. I can find more of these boards if it proves to be worthwhile.

Nick :roll:


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## daveerf (Mar 7, 2009)

To be redundant, I agree with Chris that gold plated traces on circuit boards is RARE. Extremely rare.

You will only find that on one out of a million of different types of circuit boards. It may not even be worth your time to find out which ones do have that because you will end up testing for hundreds of hours and chances are you will never find even one with gold plated traces.


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## oldtimmer (Mar 7, 2009)

Having worked in the electronics industry for 35 years, it is not uncommon to see some boards that do have gold plating under the solder mask. In the 70's and 80's you could find it more common that what you will find today. I have never seen a computer mother board with gold traces. It is not needed. Where I work we do a lot of RF testing and all of our boards have 100% gold plating on all of the copper runs. And yes if the solder mask is of a lighter green color, when used over the copper, you get an appearance almost that of there being a gold plating under the solder mask. This is very commonly seen on memory cards where the pads that are solder to are gold plated but the other runs are only copper. I am currently processing around 500 memory cards and I do a scratch the solder mask to see if the runs are gold plated. I have found only 2 out of around 250 that actually have gold plated runs. Both of these are older memory sticks probably from the 70's and 80.s.


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## lazersteve (Mar 7, 2009)

I have seen and posses many PCBs with fully gold plated runs under the green solder mask. A common card that comes to mind is the Ensoniq sound PCI cards. Another card that commonly has gold plated over copper traces under the solder mask are early 1990's ISA slot sound card plus modem and cdrom controller combo boards made by Creative.

Here' a photo of a box of boards with confirmed gold plated copper traces under the solder mask:

[img:668:765]http://www.goldrecovery.us/goldrecovery/images/goldplatedtraces.jpg[/img]

A short list of manufacturers of some of the cards are :

Kingston, Ensoniq, S3 Video, HP, and Creative.

I would not go as far as to say the cards are common, but they certainly are not rare between 1990 and 1997. Prior to 1990 the gold plated copper traces were even more common.

I've learned to quickly recognize the cards by the lighter colored edge traces that the fingers have. The gold plating (across the entire card) on them is actually thinner than the very common fingers that have a more rich golden color to the finger edge. The deep yellow fingers are typically the ones with only copper under the mask. The brighter, shiny almost white fingers are typically the ones with gold plating over copper traces under the solder mask. I'm guessing the function of this complete plating is possibly for added radio frequency shielding. 

The exceptions I have seen to the lighter colored traces have been old laptop (386-486) power boards and very old HP plotter and test equipment boards. These types have a nice rich yellow color to them across all of the copper traces under the solder mask.

Steve


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## nicknitro (Mar 8, 2009)

Thanks For all the responses guys, 

My results were from a hard drive controller board of an early 90's IBM P/S2 XT 70 computer. The wires I peeled away from the board were completely dissolved in nitric, so I would have to report a nil value.

Steve, Maybe a sticky of the boards for treasure hunters?

Thanks again 
Nick


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## Astraveller (Mar 14, 2009)

I thought some might be interested to see what we discovered today. At the beginning of this tread I took a picture of three dishes – the one on the left was a gold plated circuit board in caustic soda – we just left it there. 10 days later TonyD took another look and although it didn’t look any different he gave it a prod with a spatula and noticed that the green solder mask fell away revealing the gold plate underneath.

We fished it out, cleaned it off with fresh water and put it through the AP process which stripped it in an hour or so. The yield was low, the plating must be very thin but the process is cheap and as I have been reminded a few times ‘gold is gold’

This is great!! if we have got it right – no hot caustic – no expensive chemicals – just patience – and the process is easily ‘up scaled’.

Comments gratefully appreciated.

Linton. 

Photos below.


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## nicknitro (Mar 15, 2009)

Nice Job,

I really appreciate the update. Quick question. Lye is relatively easy to find. What was your source, chem manufacturer or store bought.

Great knowledge for future refining.

Nick


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## lamp (Mar 15, 2009)

I have a question , would any PM's be left behind in the caustic soda solution? If so what would be the best way to remove it?


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## oldtimmer (Mar 15, 2009)

In one of the post, I saw a mention of adding salt to the hot sodium hydroxide solution to help in the removal of the solder mask. I could not find any mention of how much to add.

Can someone provide any more information?

Thanks


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## Astraveller (Mar 15, 2009)

Nicknitro - We bought caustic soda at the local DIY store. 

Lamp – I do not think any PMs are left in solution but this question is best answered by others with more experience.

Oldtimmer – I don’t know about adding salt to the solution but the caustic soda we used was not heated at all. Here in the UK it’s quite cold at the moment, all we did was to leave a pc board in caustic soda for 10 days – and that was out of laziness rather than a scientific experiment. I’m hoping the big guns will show up and will ratify/explain/condemn or commend this observation.

Linton.


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## g_axelsson (Mar 15, 2009)

Astraveller, that is a great result. Do you have any idea about what concentration of caustic soda you used?

I have twice tried to treat some cards I got but never got a good result. I have a couple of kilos of clean boards with gold plate under the solder mask. It is enough to be a nuisance to store and too good looking to sell as scrap. Time to do something about it. 

Thanks for sharing!


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## nicknitro (Mar 16, 2009)

Brand Name then?

We have many similar brands out my way, however, I just wonder if yours had any additives>?


Must be further direction in your process Old Timmer


= dumb answer


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## Astraveller (Mar 16, 2009)

Hi, g_axelsson and Nick,

As I write this I am at home in the evening so do not have the bottle of caustic in front of me but I will double check the info and post a pic tomorrow if necessary. We bought a plastic bottle – the equivalent to about 250 to 500 ml (if it had been a liquid) of 99% Caustic Soda. It had ‘Caustic Soda’ in big letters on the label - please do not think I being sarcastic, I am not. There was a brand name which I can’t remember and it is probably not that relevant anyway.

The legend on the back was for two types drain clearing dilutions, we choose the stronger.

Since the variables are:- Dilution, Temperature and Time and since hot caustic is best avoided it would seem the best advice would be – get the strongest caustic you can, ‘dilute’ it to saturation point (that doesn’t make sense but you know what I mean) and see how long it takes. 

The thing is that is does seem to work.

Since my last post I have put some more boards into the caustic solution, which I beefed up a bit, and some of them have cleaned already – two days – some of the others show signs of stripping and the rest are a bit more stubborn – but they will be mine! Oh yes, they will be mine! GOLD! GOLD! I TELL YOU!! 

Ahmm, sorry about that! 

Hope this helps.

Linton.


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## goldsilverpro (Mar 16, 2009)

The saturation point of NaOH is above 100 av.oz./gallon = 6.25 #/gal = 750 gm/l. It's available in that strength in drums as 50% caustic soda - 50% water and 50% caustic soda, by weight. It's like syrup and can be nasty to work with. It's like H2SO4, as it gets hot when you dilute it. Being already liquid, though, it's mighty handy. Caustic can etch glass. Use SS instead of pryex. You'll really screw your beakers up.


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## bmgold (Mar 16, 2009)

> Caustic can etch glass. Use SS instead of pryex. You'll really screw your beakers up.




Thanks goldsilverpro. Little bits of knowledge like that makes it worth reading every post.


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## Astraveller (Mar 17, 2009)

It seems my memory is more or less intact – here are a couple of pics of the bottle of the caustic we used. Slight apologies for the focus.

Linton.


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## goldsilverpro (Mar 17, 2009)

You have the good stuff.


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## dick b (Mar 17, 2009)

I have found it as Crystal Draino in metal Canisters at Lowes in the plumbing section and as Rooto crystals of Household drain opener at the 
True Value hardware store in my area. The Rooto package says 100% lye on the front of the plastic bottle. It is a 16 oz package (454 grams)
I also buy the Rooto h2so4 gal size drain cleaner at the same True Value Hardware store.


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## oldtimmer (Mar 18, 2009)

Finally able to start another batch of solder masks boards today. After a week of prep work and cutting down boards, they went into the soup mix today.

I started with a cup of rock salt (don't know, but it was recommended in one post). I took about 1 gallon of hot water out of the tub. To this I added about 2.5 gallons of very hot water which I had put on the stove and allowed it to just start to bubble very lightly. Then took the hot water bucket outside to the side yard. I put half of the boards in. I then added a full can of Draino plus a left over half can to the water followed by the remaining boards. It took about 10 minutes for the bucket to get really hot and the mixture to boil. I took the precaution of putting the bucket inside of another one, just incase.

I checked the mix after 3.5 hours. Still a small boiling action and a lot of green solder mask floating on the top of the foam. I then very carefully removed three of the five different types of boards to check on how the removal was doing. After rinseing off these boards wit clean water, If ond that the solder mask would come off with a gentle rubbing action with my rubber gloves. I could not get to the other two types of solder mask boards as they were too far down in the bucket.

So my conclusion is that the water must be fairly hot to start and that the added heat at the start has made the difference. These are the same type of boards that I had tried before with little success. The last time the water was not as hot to start and I did not see the boiling action of the Draino that I saw this time. Did the salt help or not, I do not know, but I have acheived the results that are needed. 

I will post final results and pictures later in the week.


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## nicknitro (Mar 19, 2009)

Ya know,

I never really considered that the salt would raise the boiling temp of the aqueous solution. What is the boiling point of Lye mixed with water again ? Would salt help raise the temperature at all? 212 to 240 to 300 could make leaps and bounds of difference to stripping capabilities.

I still question the relevance of the salt chemically. The Lye already performs it's duty with heat.

Curious,

Nick


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## Anonymous (Mar 19, 2009)

Hey guys,does anyone know the effects of the lye solution on ptfe?I have a some 55 gallon plastic drums and a couple hundred pounds of gold traced boards but I really dont want to end up with a caustic soda "lake" in my backyard.Dont get me wrong,I could use a new pool,but my skin just burns a little too easy.If I dont hear a reply by tonight I'll just cut off a small piece and let it soak for a week or two and test the consistency of it.

Johnny


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## tonyd (Mar 19, 2009)

Hi
I work along side astraveller with the gold refining Tonyd

None of our caustic was heated all we done was let a small amount of plated cards sit in the caustic for a number of days and then had a look.

What we found is what astraveller posted early on in this thread.
Patience is all it takes. 




How can it be waste if someone wants it


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## Astraveller (Mar 24, 2009)

Hi guys,
I thought some might be interested in what we discovered today. We left some gold plated boards in caustic to dissolve the solder mask and today I thought it would be a good idea to clean of the ones that were ready. 

I rinsed them off and washed them in running water for a minute or so and then used a plastic washing up brush to clean of the remaining green solder mask. In the process I noticed that some of the boards were showing ‘silver’ printed circuit board as well as the gold. I sanded down through ‘silver’ to the copper underneath and then through to the green board.

It very much looks like the caustic has either 1) eaten into the gold or 2) eaten into the layers underneath and allowed the gold to lift off.

I examined both the caustic dish and the rinse dish, which I used to clean the board during scrubbing and both contained tiny flakes of gold in the sludge. I tried the stannous test on a drop of the caustic – all this did was to produce a little plume of ‘smoke’ and ‘tested’ negative.

This throws up a number of questions – off the top of my head:-

1.	Can caustic soda dissolve gold? (Doubtful – someone would have discovered that by now and it would be common knowledge)

2.	Is the caustic allowing the gold to lift off?

3.	What is the ‘silver’ layer in between the gold plate and the copper layer?

4.	Is the gold so thin that caustic and modest abrasion just wears it away like cheap thinly plated jewelry?

5.	If it’s that thin, is it worth bothering with?

6.	How do you recover and process gold flakes from caustic sludge?

7.	I read somewhere that any adversity has within it the seeds of an equal or greater benefit – does anyone see one here?

It does, however, seem that if caustic soda is to be used to prepare these kinds of boards (with or without heat) for the AP process, the caustic process needs to be monitored carefully.

I have included a couple of pics of the boards and the bottom of the caustic dish which does have gold flakes in but I am not sure how clearly they can be seen but they are there.

I would welcome any thoughts or comments.

Linton.


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## goldsilverpro (Mar 24, 2009)

> 1. Can caustic soda dissolve gold? (Doubtful – someone would have discovered that by now and it would be common knowledge)
> 
> 2. Is the caustic allowing the gold to lift off?
> 
> ...



1- NO. Nor will it eat Ni or Cu.

2- I don't see how. It could eat the adhesive that holds the copper traces onto the board material itself. In that case, though, the Au, Ni, and Cu would come off together. 

If the gold were plated on solder (Sn/Pb) plate, the NaOH could attack it and flake off the gold. I have never seen gold plated on solder plate, but that doesn't mean it's impossible.

3- It there was gold on the traces to start with - of which I have grave doubts - the silver colored metal is usually nickel. If there was no gold, it could be nickel or solder plate.

4- Possibly, but I doubt that a bristle brush would do it.

5- Probably not, whether it's thin or thick.

6- Dilute it considerably (less than about 5% NaOH) and filter it. If the NaOH is too strong or hot, it will eat the paper.


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## Astraveller (Mar 24, 2009)

Thanks GSP, that’s what I thought – for the most part!

But. 

7. I read somewhere that any adversity has within it the seeds of an equal or greater benefit – does anyone see one here?

I am a newbie.

Linton.


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## Astraveller (Mar 24, 2009)

GSP, you revised your post and expanded on it, I thank you!

Linton.


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## g_axelsson (Mar 25, 2009)

I have seen similar results on some boards that was laying in NaCl a week or more. Some of the tin or lead was dissolved an replated on top of certain traces. I always suspected it to do that because of elecronegativity of led or tin forming an electrolytic cell. Solder goes into solution while tin is plated out on the gold plated traces.

Try to put the board in HCl, it should remove the tin on top and show you the golden surface again if I'm right.

The plating is really thin and is hard to see when sanding through the copper traces. Not only that it is thin, if you have tin on top it will smear and cover any traceof gold in the sanding area.

If you have an exposed metallic area, just add a drop of nitric acid on top of it and soon you will see the plating floating around inside the drop. Then you will know if it is thin or thick plating.


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## goldsilverpro (Mar 25, 2009)

g_axelsson said:


> I have seen similar results on some boards that was laying in NaCl a week or more. Some of the tin or lead was dissolved an replated on top of certain traces. I always suspected it to do that because of elecronegativity of led or tin forming an electrolytic cell. Solder goes into solution while tin is plated out on the gold plated traces.



That doesn't make much sense to me. Tin or lead won't cement onto gold, ever. Something else must be going on. If there is gold and if the gold is very thin, it will be very porous, exposing the nickel. Maybe the Pb or Sn is cementing onto the nickel through the pores.



> If you have an exposed metallic area, just add a drop of nitric acid on top of it and soon you will see the plating floating around inside the drop. Then you will know if it is thin or thick plating.



You will also know if the gold is non-existent.


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## g_axelsson (Mar 26, 2009)

goldsilverpro said:


> g_axelsson said:
> 
> 
> > I have seen similar results on some boards that was laying in NaCl a week or more. Some of the tin or lead was dissolved an replated on top of certain traces. I always suspected it to do that because of elecronegativity of led or tin forming an electrolytic cell. Solder goes into solution while tin is plated out on the gold plated traces.
> ...



And still I have seen it... 

I was not thinking about cementing out tin or lead as silver does on copper. I was thinking in the way of electrolysis. Tin have higher electronegativity than copper, if a board with gold plated copper traces is placed in a solution with tin in solution where would it go? Would copper go into solution while tin is plated on the exposed metal surface? Why would it not attach to the gold surface?

The interesting part is that I had a number of boards from a HP computer. They only had solder mask on one side but it was fully gold plated on both sides. The gold was thick enough to be picked up in cm-long pieces once it was free of the board.
One trace could be unaffected gold and the next fully plated with a silvery metal after a week in lye. As the board was broken in parts to fit into the bucket some traces were in contact with solder on the board and some were not. I don't remember which category of trace that got the "solder plate".

I think I still have that board unprocessed. I'll take a picture when I find it but it could take a while. I'm helping a friend to clean out a 60 square meters storage space full of old computers (Norsk Data minis) and terminals. 
If I haven't posted a picture in june, just remind me.


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## butcher (Mar 26, 2009)

In the electromotive series tin is higher in series than copper, 
so if both are in an acid of say copper ions disolved, the tin would dissolve in the acid and precipitate the copper as the tin loaded the acid.

If two metals are in an acid say copper and gold the gold would try to plate to the copper. the metal lower or less reactive would try to plate to the more reactive metal, (not the other way around).

And the more reactive metal will displace the less reative metal from a solution, try doing a little study on this it is such a important part of what we do, understanding it can help you solve problems.


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## g_axelsson (Mar 27, 2009)

Whooops! My bad!

I was looking on electronegativity and not electrode potentials. Dohhh! 
It was a long time since my last chemistry class.

The right table to look at is this one.

But still, I have a few silvery traces on my broken boards. I'll have to examine it in detail and stop guessing.


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## wop1969 (Apr 10, 2009)

To add to this post, I found a dark colord sound blaster live card and dropped it in a bucket with about 8 cups of water and 4 healthy tablespoons of crystal draino (LYE) I did heat the water with the coffe maker first, their was allot of boiling noise and the bucket got very hot (had it in a pan) and then the reaction stopped.

2 days later I pulled it out and sprayed it with the water bottle on streem and everything rinsed off with no effort.

I will strip a piece of trace and run it and test it and post my finding.
The card was a sound blaster live, if anyone knows if they covered in gold or not, please respond, I will post my findings otherwise.

One more thing ,the traces on the finger are the same color as the rest of the board, and I know the fingers are gold but a test is still in order.
Here is the finished results.


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## texan (Jan 27, 2011)

There is another post that covers this but just a reminder that lye (caustic soda) is nasty stuff and ALWAYS use chemical gloves and safety glasses. Don't get sloppy around it...one small drop in an eye can do major damage.

Texan


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## Harold_V (Jan 28, 2011)

texan said:


> There is another post that covers this but just a reminder that lye (caustic soda) is nasty stuff and ALWAYS use chemical gloves and safety glasses. Don't get sloppy around it...one small drop in an eye can do major damage.
> 
> Texan


A very good admonition, Texan. Thanks for bringing up the subject. 

Years ago I had the misfortune of having a drop of nitric acid splash in my right eye. I was alone, and couldn't see from that eye (the surface of the eye turned yellow and shed almost immediately). I drove myself to an ophthalmologist, who informed me how lucky I was. I didn't think so, but he went on to inform me that had the drop been lye (sodium hydroxide) I most likely would have lost the vision in the eye. I was told the eye would return to normal, which it did. A valuable lesson in wearing safety gear, one that I didn't really need to learn, for I was already aware of the stupidity of working without eye protection.  

Wear the safety gear, folks.

Harold


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