# Gold loss removing solder mask?? HELP PLEASE a NEWBE



## dan63 (Jul 8, 2012)

Loss of Gold in NaOH… Please help… I’VE SEARCHED AND READ… but have not seen anything related to what I’m seeing. I have over 100 printed circuit boards some of them are solid gold plate on one side (30 square inches) and gold plated traces on the other plus the typical gold fingers. I have removed the solder mask using a 20% solution of NaOH (500ml of H2O and 125g of NaOH flakes). I boiled at a slow boil for about 5 minutes. The solder mask came off ok… BUT…
Here is the problem: some of the large areas that were gold in color are now silver. HELP…. One of two things is happening; either I’m getting some form of tin/lead plating or I’m losing my thin layer of gold and exposing a layer of tin below? From my limited knowledge for Chem. NaOH is”looking” for another H ion, and will form some type of salt and water. NaOH should have no effect on Gold. So if I’m losing the gold into solution why???? is it due to heat and a very thin layer???? I processed several batches, the first three or four batches the solder mask came off easily after that each batch was a little less effective. But ALL batches of boards have some amount of silver where there had once been gold… this may have gotten a little worse with each batch???? Hard to say. 
If this is just a platting issue it will be dealt with in the AP process and should not be a problem BUT if I’m losing Gold into the solution of NaOH then I have a worse problem… I did take a bit of HCl and rubbed it over some of the “silver areas”(in hopes of removing the tin/lead) however I did NOT see the gold color return so I thinking I’m losing my Gold into the solution of NaOH… I don’t think I can use stannous chloride on the solution of NaOH right???? any ideas???? 
Maybe I should use a different approach all together, I could first remove what I can of the exposed gold using HCL/CL or AP then treat the boards with NAOH to get at the Gold under the solder mask and then go back to HCL/CL or AP ?????? What are your thought folks?????? And thanks so much for your help!!!


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## etack (Jul 8, 2012)

Why do you think that you have gold under you solder mask?

did you scratch off some or are you seeing gold color.

lye wont eat your gold most likey you didn't have any.

Post a pick of your boards.

Eric


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## dan63 (Jul 9, 2012)

these boards are a little unusual. many have full gold fields on one side and have the traces on the other. the solder mask is also in many cases only on one side. and Yes I have scratched the solder mask off and verified that the gold is also under the solder mask. in most cases the areas that have turned silver are only portions of a gold "field". I'm very puzzled by this. is there a possibility that there is some chemical in the solder mask that could attack the gold?? I know NaOH can not. or is there a chance that some of the tin in residual solder is plating areas of the gold. I'll post some pics in the am. thanks for your help.


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## Geo (Jul 9, 2012)

unlikely. strong bases will discolor gold if you let the temperature get too high. it doesnt really dissolve it at all. take a rough piece of cloth and give the discolored spot a good rub. if the gold doesnt show back up, you can always apply a drop of nitric acid. ive seen cards that had gold traces showing on many spots only to remove the solder mask and find copper under the mask. the gold traces will still be there, but the areas under the solder mask would be bright red.

good luck.


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## dan63 (Jul 9, 2012)

Ya I've see that too, mostly on newer boards esp. Ram cards where the fingers are gold and the pads that the parts are soldered to are gold but the ares under the soldermask are copper.... I've been in the electronic industry for 30 years... worked for HP for 20, The boards I have are full gold plated under the solder mask..

I was thinking about this last night while trying to sleep... lol Is there a possibility that the field around the burner is setting up eddy currents in the foil and causing a reverse electroplating??? It really looks like I've lost a lot of Gold... I sure hope that you are correct and it has just discolored but it is a nice bright shinny silver where it once was Gold. I'm thinking I've exposed a nickle or tin layer between the Gold and Copper. OK looking forward to replies I'll sit back here and not get too worked up LOL and continue reading.

Does anyone have an idea how many boards I can process in 500 ml of 20% NaOH the boards are roughly 3.5X10 and most only have solder mask on one side?? can I keep running batches unit is no longer effective or am I reaching considerations of some chemical that is causing me grief at higher temps????? thanks so much for your time!!!!!!!


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## maynman1751 (Jul 9, 2012)

I don't understand why either, but I have lost gold while removing mask also. I was removing mask from ram sticks and when they came out the gold that was visible before was pretty much gone! I wondered if perhaps I left it in the solution too long, like overnight.
I've also had gold removed while soaking ram sticks in warm HCl to remove the chips. This is not supposed to happen either! :?:


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## goldsilverpro (Jul 9, 2012)

Have you ever had success getting gold from under the mask on ram sticks?


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## Palladium (Jul 9, 2012)

What may be happening is you are not using a high enough concentration of sodium hydroxide. Tin will dissolve in NaOH and then plate back out on your gold. If left to long it will make the gold traces start to release the foils. Did you do a pre wash in hcl first? Ammonium should clean up any tin that has precipitated on the gold The process does not take long and should not be left over night. You need the solution hot for it to work fast before it starts too cause trouble. Add the boards first then water that has already been premixed with NaOh being careful not to splash it on you or your skin, especially your eyes, then heat. Use fresh NaOh for each new batch. Hot NaOh is nothing to play with!


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## dan63 (Jul 9, 2012)

@ goldsilverpro
I have never seen any gold under the mask on RAM sticks the only place I've seen this is high end test equipment from the 70s and early 80s by the 90s any gold plate under solder mask is so thin the AP process may not be the best way to go at it. 

with very thin gold plate it may be better to use HCL/CL or AG... I never done this but it just seems like there is less chance of lost valuables if you are dealing with a solution and are not trying to deal with small flakes... I'm just thinking that with VERY thin Gold plate even in AP some of it goes into solution and if the gold plate is thin enough you may not have any visible flakes to work with????????? does any one have any experience with this????? would love to hear from experience rather than my theory!!!!!


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## BAMGOLD (Jul 9, 2012)

I'm pretty sure I have at-least 1 ram stick with Gold Traces out of 100 sticks or so.


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## Palladium (Jul 9, 2012)

I ran several lbs of gold plated ram here awhile back. The gold plating thickness under the mask is almost not worth it in a way unless i had some serious weight. Now the fingers were pretty good as i remember. Matter of fact the gold under the mask started releasing from the boards during the NaOh phase on me and i had to change my whole process around. I used NaOh as a type of ap i guess. Then i run them for a soak in warm ammonia, wash, then dissolve the foils. Comes out fairly darn clean on the first drop. Of course i ran everything pretty much twice. I figure the coating of gold is released because it is so thin and the NaOh dissolves the layer of gold it's plated on. That's my theory anyway! Don't know what type they were, where they came from or where they were headed but some old gentleman drug them up and brought them to me.


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## maynman1751 (Jul 9, 2012)

goldsilverpro said:


> Have you ever had success getting gold from under the mask on ram sticks?



Hey Chris! My intent was to remove the mask to try to release the tiny 'tubes' that would be solder points on the ram. I've had some success. I know that it is not a large amount of gold retrieved by this, I just wanted to see. I figured that I may have left it too long in solution. Also, I was using potassium hydroxide. I don't know if that makes any difference, but it does basically the same thing. This was a first for me......live and learn. And yes I know this is some bad--- stuff!


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## Geo (Jul 9, 2012)

if you remove the solder mask and run material through AP, filter all solids (even boards if its ram), rinse well and place in a glass container. add a little hcl making sure all material is wet with hcl. add bleach and cover. the chlorine gas will dissolve any gold (even in the little holes)put a lid on and give it a few good shakes.filter solution and rinse solids. add rinse to the filter. of coarse it will be dirty, but you didnt lose any gold. the trick is to make sure all the base metal is gone. of coarse test the solution with stannous chloride before proceeding. a negative result means base metal is still present and the gold cemented out. even with a positive, i would still give it one more rinse with hcl/Cl just to be sure.


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## artart47 (Jul 9, 2012)

Hi. 
I've had the same thing happen. They are cell boards other items with very thin gold and it just disintegrated.
I left the bucket sit and all the liquid has evaporated leaving a mas of lye crysals solder mask debris and has a dingy color.
The gold is in there!
When I get a chance, I'm going to slowly drip HCl into it to get rid of the lye HCl+NaOH----> NaCl+H2O. I should be able to wash it with water to disolve the salt andlet the solids settle. They sold contain any gold. then boil in HCl and a little sulfuric acid to rid it of base metals.
Just remember that these type of pieces have very little gold even though it looks like alot and you may barely be able to see the gold even after it's recovered. I was thinking of continuing to use my lye bucket untill it contains alot more gold before attempting to recover it.
Also! If you search my posts I had some responces from others on this problem.
Hope this helps!
artart47


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## dan63 (Jul 9, 2012)

I'd like to post some pics so you all can see what I'm seeing... I did a search on how to post pics on this sight but not much came up... can someone let me know how to post pics... do you up load them directly or do I need to upload them to some other server and just provide a link/URL???? 
thanks


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## Geo (Jul 10, 2012)

when you "Post Reply" theres an option below the box your typing in that says "If you wish to attach one or more files enter the details below" click "Choose File" to find the picture or file on your device and then click "add the file".


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## maynman1751 (Jul 10, 2012)

Geo said:


> if you remove the solder mask and run material through AP, filter all solids (even boards if its ram), rinse well and place in a glass container. add a little hcl making sure all material is wet with hcl. add bleach and cover. the chlorine gas will dissolve any gold (even in the little holes)put a lid on and give it a few good shakes.filter solution and rinse solids. add rinse to the filter. of coarse it will be dirty, but you didnt lose any gold. the trick is to make sure all the base metal is gone. of coarse test the solution with stannous chloride before proceeding. a negative result means base metal is still present and the gold cemented out. even with a positive, i would still give it one more rinse with hcl/Cl just to be sure.


Thanks Geo! That's basically what I was doing although I tried spraying the 'tubes' out with my spray bottle and that worked relatively well. It was more labor intensive, but I wanted to see how much I could recover and if it was worth it. Some of those ram sticks have quite a bit of gold that most people don't bother with! To me, with my limited resources, I find it rewarding to ferrit out every bit I can. It's just a hobby.....and it's fun. I don't plan on making any real profits.......maybe someday.
Thanks Again Buddy!


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## Marcel (Jul 10, 2012)

1. Hot NaOH can dissolve Gold (but very unlike unless you don´t take it to the top concerning heat, NaOH concentration,time) 
2. Hot NaOH will dissolve basemetals such as tin oder Pb.
3. These dissolved basemetals will be cemented back onto gold plated areas and make them appear in a different color ( usually black)
HCl + a bit H2=2 should remove this layer.

*But* in addition to that, many areas that lie underneath the solderresist look golden because of the color that is in the solderresist. Once removed it is only copper.
Green(Solderresist)+Red(Copper)= Yellow/Golden.....
it is called additive color.
http://en.wikipedia.org/wiki/Additive_color

I have been tricked by this effect several times.


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## dan63 (Jul 11, 2012)

Wow thanks so much for all the feed back
I have found out a bit more as I've experimented:

first I'm more sure it is Gold loss and not plating over the gold... and I think the reason for it is evaporation of H2O as I run boards through the solution of NaOH... should have been obvious to me... 

The concentration of the NaOH is approaching 30-35% by the time I run 6 or 7 boards through at roughly 5 minutes/board. I know not all the loss of solution is due to evaporation but there is enough water loss that my concentration has to be rising as I run batches. I've been using a large flat glass baking dish to accommodate the size of the printed circuit boards... this provides a lot of surface area for evaporation. I never see this gold loss with new batches of NAOH it is only after I've run several batches. I'll have a chance to verify this with my next batch. If I can prevent Gold loss by adding a bit of H2O it will pretty much settle the question in my mind. 

but that does lead to this question: does anyone know at what concentration levels of NaOH Gold will go into solution? 

as for the question of gold plating under the solder mask... the boards I'm working with HAVE gold plating under the solder mask. I know now days this is not a common practice but when I first started working in the aerospace electronics industry it was a common practice for several manufacturers. at the time it was considered "best practice" although time and technology would change all that!!! lol 

Geo thanks for the file upload info not sure why I didn't see it!! ... Pics to follow!


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## dan63 (Jul 15, 2012)

OK it seems I've worked through my trouble with NaOH. following are some suggestions to prevent problems:

1. as Steve indicates, a 20% solutions works well on most types of solder mask. There is one type of solder mask I found... it is a blue green color, comes off after about 10-15 seconds in hot 20% NaOH and makes a mess of the solution. I found that a 10% solution works best with this type of Solder Mask, and it only takes about a minute before you can easily rinse it off with water. there is a another type of solder mask that is a clear yellow green that turns into about 1/8 inch of slim and makes a real mess... not easy to get off... may not be worth your time!! it has a very unique look to it and out of more than 100 boards there were only 2.

2. the smaller the board size the better, this minimizes the size of container you have to use to heat the NaOH and reduces evaporation. I found it best to cut larger boards down to a 3x5 inch size.

3. try to keep the temp just below boiling. 210 F seemed to work very well, however a few boards took 7+ minutes at this slightly lower temp.

4. if the solution of NaOH becomes thick with dissolved solder mask it is PAST time to start a fresh batch. it really seems to me that the more solder mask in solution the more trouble I had with Gold loss. I don't have an explanation for this. I also think that this is secondary, and the primary problem was an increase in the concentration of NaOH due to evaporation of water. I'm also not convinced that fields set-up by the electric burner inducing eddy currents in the foil were not in part to blame. I say this because of the pattern of gold loss on the boards. I plan to try a gas burner and see if that changes anything.

5. I can not stress enough the need for ventilation when working with this stuff!!!!! I worked outside and even set a fan in place to move fumes away. But a hood really is what should be used!!

As I'm typing I'm also realizing that this may not be very useful info to most people... it is not often that you find boards with gold plated traces under solder mask. 

my next step is to run the AP process on a few of these boards!!! wish me luck!!!!!

I did a search of the sight in advance as I'm afraid of losing more Gold in solution. I did not see much specifics on what to do with Gold in AP solution... I know most won't go into solution, but I've already lost a bunch, so I'm more concerned and given my luck so far... I want to do what I can to avoid this...

In Steve's video on the AP process, he states that some of His gold went into solution and that he would have to use SMB to precipitate it. later he stated that the "copper pushed the gold out of solution. Is this pretty much always the case? Or only the case with AP that has been in use for a while and has higher levels of copper chloride in solution?? There is something I'm missing here... I'll do a review of lit. I'll for sure test with stannous chloride... but if I have a gallon to gallon and half and I end up with gold in solution what is the "best practice" steps to recovery. OK OK maybe I should not even give it a second thought and cross that bridge when/if I come to it.

thanks again everyone I'm learning a lot, and hope to one day provide useful info to other beginners.


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## butcher (Jul 15, 2012)

Gold will not dissolve in the copper chloride leach (called acid peroxide), the gold is too un-reactive, unless you oxidize the gold with the use of too much oxidizer in the copper chloride leach (such as too concentrated hydrogen peroxide solution), now the oxidized gold can form a gold chloride in solution, adding more copper to the copper chloride leach will dissolve more copper and solution will begin to change from a copper II chloride (green) to a copper I chloride solution (brown), once saturated the copper I chloride salt will begin precipitate (white powder), also if you did have any gold chloride in solution it would plate out to any copper that the copper II chloride leach was trying to dissolve (Gold would look like brown powder) or if the solution was converted to a copper I chloride (brown) the gold would precipitate as brown powder, most likely mixed with the white copper I chloride salts.

I see no need for the use of SMB in the copper chloride leach, control the amount of oxidizer used, and if you use too much just add more copper to the solution to push your gold out of solution.

Using SMB would make your copper chloride leach useless, if you do not use the SMB you can rejuvenate and reuse the solution as a leach.

Laser Steve Has an excellent document of this leach and treating the solution on his web site.


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## golddigger2 (Jul 18, 2012)

Hot sodium hydroxide will remove solder mask. Warm it slowly to boiling, put in your boards, boil for 5 mins, remove and wipe off the green goop. Wash well with fresh water. Job done. Wear gloves, eye protection and avoid breathing the steam


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## dan63 (Aug 7, 2012)

this post is to follow up on my last post and to plead for help I'm sure not having beginners luck:

I processed all my boards using the AP process and collected 15.3 grams of gold flakes. I ran a small batch of this in HCL/CL this formed the typical clear yellow solution. I then heated the auric chloride to drive off excess Cl, and let it sit over night. the next day I added SMB and precipitated the gold, after 24 hrs I had a thin layer of gold on the bottom bottom of the beaker. I siphoned off most of the liquid and am drying it... good so far!!

Everything seemed to go OK with this test batch. So I decided to proceed with the bulk of my gold fingers/traces (about 14 grams). It was a disaster. when I added then Cl to the HCl a large amount of white precipitate formed?? from the reading I've done I decided it was a copper chloride salt. I filtered it off and was left with about a gallon of Auric Chloride. I separated this into 3 smaller containers(beakers) to process it further.

This is where things went real bad!! While heating one of the beakers of Auric Chloride, the beaker broke! I was working over concrete and was able to mop it up, but I have a real mess. My first thought was to toss it, but I think it would be a very good learning experience for me to try to recover it. (once all the Cl has dissipated I plan to add water to the area of the spill and used a clean wet vac to pick what I didn't get while moping) I now have about 2.5-3 gallons of dirty water with what I HOPE is still about 5 grams of gold in it.

I've done a little more reading and here is what I think I need to do: HCl reacts with concrete and I saw some brown color form while I was moping it up... also there was a large amount of Cl liberated at the time it spilled. So some if not all the Gold came out of solution... However I DON'T think it is safe to assume that ALL the Gold precipitated out. (it is too dirty to tell by the color) so I'll test with stannous chloride but I have to assume that I picked up so much junk that it may not be an accurate test???? At this point If i'm way off base can someone please direct me. I think to proceed I have to have all the gold either in solution or as a solid, but not both. and I think it would be easier to manage the contamination if the gold was NOT in solution.... after I have all the Gold back out of solution from my reading I think the next steps would be:

1. Let the "slop" settle and siphon off as much liquid as possible. this assumes that there is no gold in solution (I'll test with stannous-chloride) If gold colloids have formed I'm at a loss.... Please help!! (I just read the thread "Tin in AP" and that was helpful with dealing with gold colloids)
2. I have to assume that I have every kind of contamination possible. I know there is a bit of sand/small rocks, dirt, bits of organic material + metal filings of different types etc. once I have all the liquid removed from the solids I thought to incinerate/roast using a torch (I have a propane torch) to oxidize any additional base metal and burn off any organic material I picked up. 
3. next I think I need to wash/boil with HCl (and maybe a bit of sulphuric acid?) after boiling with acid. I should also add water to the solids and boil. this should remove the base metals
4. after removing base metals is it OK to mix the entire mass of solids with HCl+Cl and filter out all the solids? or when the HCl reacted with the concrete did I pick up minerals that I also need to deal with???? I'm sure I now have some CaCl in solution. I found the following reaction of HCl and Concrete. 2 HCl + Ca(OH)2 -> CaCl2 + 2 H2O. this would neutralize the acid when it spilled and the gold would precipitate right??? but are there other contaminants I'm not considering???? 


I'll keep reading and between that and any experience others may have had I hope to recover the majority of this Gold... but more importantly it will prove to be a very valuable lesson/learning experience. The beaker was new and I was using a small backpacking stove but clearly It heated unevenly as the bottom popped out. I've never seen this happen before???? and did not think it possible???? next time I'll heat more slowly. 

OK If I'm way out of line and I missed reading something that deals with this already I'm sorry. I'm truly doing my best to learn and not use people as a crutch. thanks everyone for your help so far!


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## Harold_V (Aug 7, 2012)

To begin with, you you're heating beakers with direct contact with flame, you got what you should expect. They don't tolerate that well. You should have an isolating pad between the two. I used to use asbestos, which is now pretty hard to find. There are other substances, but get something before you try heating again.

The solutions. 

Allow the fluids to settle well. Assuming they test positive for gold, siphon them off, and precipitate what ever gold is contained within. Properly discard the solution after testing, to ensure you have recovered all of the values. 

You now have solids remaining. Get them all in a filter. Don't be concerned about what is contained within. The resulting filtrate is likely to contain traces of gold in solution. Precipitate and wash properly, and discard the solution, as you did with the large volume. Be certain to test the solutions with stannous chloride, known to work. 

You now should incinerate the solids. Filter paper and all. Incinerate until there is no carbon remaining. Screen, to remove large objects, none of which should be gold. You would then subject the resulting solids to a hard boil in HCl. Add water, allow to settle, then siphon off the solution, leaving behind ALL of the solids, even fine particles. Rinse well, allow to settle, and siphon once again. 

If the rinse was free of color, proceed to dissolve the values. You have now eliminated the large volume of solution and have concentrated the bulk of your values. Examine the concrete. If it was subjected to light, it will likely turn purple. That represents gold lost. It may or may not be much. 

You have leaned a valuable lesson. Do not heat lab ware directly, with the exceptions of, perhaps, test tubes. Beakers do not enjoy the uneven, rapid heating, although they will tolerate heat well if it is applied slowly and uniformly. 

Harold


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## yar (Jun 19, 2013)

Harold you mentioned using an isolating pad like asbestos between the lab glass and heat source so as not to cause the glass to break or shatter. I have pieces of tempered glass from microwaves that I was thinking of using for this purpose on my hot plate. Do you think that would work ?



Edited to use proper terminology


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## kkmonte (Jun 19, 2013)

I'm surprised no one has responded with the "Put everything away and read more, read hoke, etc. etc. etc.". 

Dan63, not trying to be offensive, however it doesn't seem that you accept any answers you are given. You ask your questions looking for an answer and when someone (from page 1) posts a response, you dismiss it by saying "Nope, I know it's not that!", or something similar. Have you read all of Hokes book? Have you performed the getting acquainted exercises? Seems to me if you keep going the way you are going, you are only going to hurt yourself or possibly someone else.


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## FrugalRefiner (Jun 19, 2013)

Uh, guys, This is an old thread.

Yar, I wouldn't advise using that piece of glass on your hotplate. Find yourself a Corningware Pyroceram dish.

kkmonte, Dan63 hasn't been on the forum since Sept 13, 2012.

Dave


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## kkmonte (Jun 19, 2013)

ARG ! I didn't even look at the dates! LOL, i just saw it at the top of the new posts.. haha It's all Yar's fault!


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## yar (Jun 19, 2013)

Yes it was an old thread which is what us newbies should be reading through, just wanted to see if my idea would be feasible. I figured if tempered glass can withstand breaking in a microwave it could be used on a hotplate. Thank you for the response Frugal...now back to the books for me.


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