Fossil preparation through chemical treatment using potassium hydroxide.

[Lmshoemaker]

PART 1.

Greetings all, it has been quite a while since I've posted here. I recently purchased some potassium hydroxide (KOH) flakes from Amazon for fossil preparation purposes. I was told about this chemical as a substitute as Quaternary-O by my friend Gabe Ward. This stuff is basically a really strong base that works (I think) through oxidizing ogranic compounds in a rock. This makes it particularly effective on shales and siltstones, but not so much with most limestones, especially crystalline varieties. I wanted to write a post about this stuff because it seems like it has the potential to be a cheap alternative to air abrasion or scribing in some cases. 

 

Safety:

 

The first thing to know about KOH is that it is a pretty powerful base, meaning this stuff is pretty hydroscopic and reacts readily with water. It is very toxic, and eye-wear and gloves should be worn when handling. Don't allow this stuff to make contact with your skin. I am a bit lax with how I handle it, and have gotten it on my arms on one occasion. You don't feel it at first, but after several minutes you will feel it burn and blisters will develop. It seems to have even burned off some of the hairs off where it made contact. This was pretty minor, seeing as I caught it, all burning and blisters went away about half an hour after washing it, but this should give you an idea of what it can do. The container on my KOH says that it produces fumes. I've noticed no ill effects, but it's something to keep in mind. This is all I wanted to do regarding safety, just give an idea of what this stuff can do. 

 

Usage:

 

The potassium hydroxide I purchased came in the form of pellets. I apply it by taking tweezers and placing the flakes on the matrix covering the fossil. When left out, the KOH will react with water in the air and start to dissolve. During this time it reacts with the matrix, and you may depending on the lithology, see some evidence of the reaction during this time. Depending on the reaction speed, I may leave the fossils out for one to eight hours. Here is one example, a set of Pentremites conoideus from the Somerset shale fm. of Kentucky. The photos aren't great, but hopefully illustrate what this stuff can do. These are separate specimens, but the one on the left illustrates a very similar "before" condition, that the one on the right was in. My next reply will address some adverse effects, and some other thoughts.                     

 

[Lmshoemaker]

PART 2.

 

So there are some adverse effects that I have noticed to using potassium hydroxide. The first is that it can bleach fossils. In one plate, I had a small brachiopod that had a flake put atop it. After about four hours the flake had dissolved, and revealed that the brachiopod underneath had lost its color, going from black to a milky clear color. Another effect is that this reaction can produce a white residue atop some fossils that is almost impossible to wash off. Superficially, it looks like the fossil is bleached, as was the case with a few trilobites I had tried this on, however it seems like it is a salt that is produced as a byproduct of the reaction. I don't really know what causes it to be honest, but there is a way to fix it. Out of curiosity I put some hydrochloric acid on the "bleached" trilobites to see what it would do, and interestingly, it removed the residue. The trilobites went from a flour white to a chocolate brown again. Pictured below is another Pentremites conoideus which has the white residue coating it. 

 

Depending on what the sediment contains in terms of siliciclastics or pyrite, there can also be some interesting effects. The plate that had the trilobites I experimented on was actually the counterpart, or underside of a plate that had a crinoid holdfast that grew on the trilobite molts. This plate had a bryozoan growing over the holdfast, and atop of it, a pyrite mat. Like the organics in the shales, the KOH will also oxidize pyrite and any other iron bearing minerals in a rock. Pictured below is the holdfast, showing the deterioration of pyrite evidenced by red/orange staining. The photo isn't the best, but illustrates the point. 

 

 

 

Also, just to show it off, here is the trilobite plate that attaches to the underside of the holdfast:

 

 

The last thing I have noticed is that a KOH treatment can discolor sediment. This effect is really inconsistent, in some cases it is clear that the sediment has been oxidized, and will show more red or yellow that presumably can be abraded off. In other specimens however, the effect is the opposite of brightening the sediment, and it will in fact darken the matrix up. This may be due to the removal of a weathered surface, but it is hard to say. I hope this post has helped anyone. Potassium hydroxide can be bought easily off of amazon or other places online. I got a 1Ib container for roughly 20 USD.

[Kane]

Thanks for this excellent and interesting guide. I am tempted to give this a try. 

 

The trilo plate is quite lovely, by the way.

[Lmshoemaker]

7 minutes ago, Kane said:

Thanks for this excellent and interesting guide. I am tempted to give this a try. 

 

The trilo plate is quite lovely, by the way.

 

Thanks, this material is certainly interesting to work with. I would recommend giving it a try.

[Kane]

Barring the use of, or access to, hydrochloric acid to remove the alkaline salt residue, would perhaps a strong vinegar solution work? I'm not sure if you've tested that yet.

[Lmshoemaker]

13 minutes ago, Kane said:

Barring the use of, or access to, hydrochloric acid to remove the alkaline salt residue, would perhaps a strong vinegar solution work? I'm not sure if you've tested that yet.

I haven't tested vinegar, so I don't know if it would work. My guess is that it would though. If not I would try some form of strong acid, using the chemistry definition. Hydrochloric, sulfuric, or something similar.

[crinus]

I have used this technique and it does work in some cases.  One thing to be aware of is that you will be using lots of water to wash the specimen.  So the matrix better be able to stand up to water.  You should not use this technique on Arkona Shale (Fm.) fossils.  I wouldn't use it on Silica Shale or Rochester Shale unless you want the specimen free of matrix.  Like cleaning a Paraspirifer.  Works great on loose specimens but think about it if you are going to try this on matrix specimens.

Also, this technique may require many repeats of applying KOH before you start seeing results.  I have been applying KOH to one plate of crinoids I have for about a years (once a week). IT is showing results but they have been slow in coming.  Why use this technique? NO damage due to abrasion. It is good if you are trying to preserve some fine detail.

Joe

[Lmshoemaker]

21 minutes ago, crinus said:

I have used this technique and it does work in some cases.  One thing to be aware of is that you will be using lots of water to wash the specimen.  So the matrix better be able to stand up to water.  You should not use this technique on Arkona Shale (Fm.) fossils.  I wouldn't use it on Silica Shale or Rochester Shale unless you want the specimen free of matrix.  Like cleaning a Paraspirifer.  Works great on loose specimens but think about it if you are going to try this on matrix specimens.

Also, this technique may require many repeats of applying KOH before you start seeing results.  I have been applying KOH to one plate of crinoids I have for about a years (once a week). IT is showing results but they have been slow in coming.  Why use this technique? NO damage due to abrasion. It is good if you are trying to preserve some fine detail.

Joe

 

Absolutely. Just to add to your comment about washing specimens. I have rinsed some for ten minutes and then soaked them for another ten, and they will still sometimes have a faint bleach-like smell to them afterwards.

[Ludwigia]

This is certainly a good method which can bring excellent results as long as the fossil is completely calcified, silicified, or composed of any substance which the KOH won't dissolve. You have to watch out for gaps in the substance, otherwise you could be in for an unpleasant shock if you leave your fossil overnight. It's always best to check on the progression of dissolution every hour or so. A Swiss friend of mine has all the equipment he could use, but he prefers to use KOH on his ammonites. The results after sometimes weeks of patient handling are just this side of stupendous. I usually just don't have the patience to use this method and only use it if it's certain that my abrader would damage the fossil.

[Doctor Mud]

Thanks for sharing @Lmshoemaker very interesting. I hadn't considered alkali treatment for pre Quaternary fossils in consolidated sediments before.

 

I use KOH a lot to break down lake sediments - to defloculate the mud. The sediment can be bound together with organic material in various states of decomposition and the KOH dissolves it.

We also use NaOH to strip out contaminants from fossils prior to radiocarbon dating. Humic acids can percolate down in the sediment and make fossils appear too young.

 

i don't have any experience with KOH on fossils in rock, but a couple of things I've learned from using many chemicals from different types of sediment processing.

 

I always try to understand the chemistry of the reaction - how will this achieve what I want? What are potential problems? Different specimens can react quite differently so a test subject is always a good idea.

 

i wonder if putting the pellets on directly is the best approach? This would avoid having to use a solution if you want to avoid this but means you have no control over the concentration. This could be the cause of some adverse effects. Are you using a 90 % solution where a 10% will suffice? I usually use 10% on sediments.

[Kane]

This is certainly something I would be willing to try on a few dispensable test pieces, particularly Windom shale. KOH is a common soap-making ingredient, and is fairly cheap (I used to make soap and detergents at home). 

 

Thanks again for writing this up!

[minnbuckeye]

How important is ventilation? Can one use these in my basement workshop with minimal air flow??

[Doctor Mud]

1 hour ago, minnbuckeye said:

How important is ventilation? Can one use these in my basement workshop with minimal air flow??

I would recommend to anyone using chemicals to look up a material safety data sheet or MSDS, such as this:

These show all the possible negative effects and relevant precautionary measures for using chemicals.

 

keep in mind you will at best create a caustic vapor and at worst create something else through a reaction with the matrix. Toxicity depends on the concentration.

I heat my KOH solution and work in a fumehood.

With a dilute cold solution you might be ok but if it was me, I would do it in a ventilated space to make sure.

 

 

[RJB]

Dont know if I will ever try this, but sure is interesting. 

 

RB

[Malcolmt]

Interesting but it might just be outside my safety comfort zone.

[Ludwigia]

4 hours ago, Doctor Mud said:

 i wonder if putting the pellets on directly is the best approach?

We get the substance in platelets here. Some place them directly on the fossil and just wait for the moisture from the surrounding air to be absorbed, which takes some time depending on the humidity. Others add a drop or 2 of water, which dilutes a bit more.

 

33 minutes ago, Malcolmt said:

Interesting but it might just be outside my safety comfort zone.

Believe me, Malcolm, it's not at all dangerous if you follow the simple ground rules.

[caterpillar]

KOH is the most common process to clean echinoids. But take care. You must rinse a lot with water after using and very good neutralize with an acid (white vinegar for ex). In some case an echinoid can be destroyed few years after treatment

KOH doesn't like cyanoacrilate. If you put KOH on a glued fossil, you can see a deep orange deposit very hard to clean

After all, it's a very good product to clean calcified fossils in marl

[Uncle Siphuncle]

I've used this stuff on Cretaceous echinoids quite a bit.  Keep in mind that the reaction is strongly exothermic and can create microcracks in the test as a result.  To combat this, I tend to heat the echs slowly in water prior to KOH treatment so as not to set up a thermal shock gradient through the specimen.  

 

As alluded to higher in this thread, voids in the specimen can allow KOH to penetrate and undercut the test, leading to exfoliation.

 

My personal preference is to lean hard on mechanical methods, using KOH as a last resort.  I'm not into chemical clean up as a sloppy job can put family or pets at risk.  And casually rubbing an eye with a contaminated finger could leave me tapping the ground with a red tipped white cane.

[Peat Burns]

22 hours ago, crinus said:

I have used this technique and it does work in some cases.  One thing to be aware of is that you will be using lots of water to wash the specimen.  So the matrix better be able to stand up to water.  You should not use this technique on Arkona Shale (Fm.) fossils.  I wouldn't use it on Silica Shale or Rochester Shale unless you want the specimen free of matrix.  Like cleaning a Paraspirifer.  Works great on loose specimens but think about it if you are going to try this on matrix specimens.

Also, this technique may require many repeats of applying KOH before you start seeing results.  I have been applying KOH to one plate of crinoids I have for about a years (once a week). IT is showing results but they have been slow in coming.  Why use this technique? NO damage due to abrasion. It is good if you are trying to preserve some fine detail.

Joe

About how long does this technique take for Silica Shale brachiopods  ("loose" specimens) to clean the matrix out of the plications / striae, etc.?  Does it take more than one application?

[Doctor Mud]

5 hours ago, Uncle Siphuncle said:

I've used this stuff on Cretaceous echinoids quite a bit.  Keep in mind that the reaction is strongly exothermic and can create microcracks in the test as a result.  To combat this, I tend to heat the echs slowly in water prior to KOH treatment so as not to set up a thermal shock gradient through the specimen.  

 

As alluded to higher in this thread, voids in the specimen can allow KOH to penetrate and undercut the test, leading to exfoliation.

 

My personal preference is to lean hard on mechanical methods, using KOH as a last resort.  I'm not into chemical clean up as a sloppy job can put family or pets at risk.  And casually rubbing an eye with a contaminated finger could leave me tapping the ground with a red tipped white cane.

Good point @Uncle Siphuncle

Im always surprised when I make up a solution of 10% KOH. Just adding the pellets to water is exothermic, I guess it's energy being release as the KOH disassociates into K+ and OH- ions with heat being released when the bonds are broken. It gets quite hot, never measured it but could be 70-80 degrees C.

[Peat Burns]

Thanks @Lmshoemaker for sharing this.  Tried it out this afternoon with promising results.  All I had around was KOH pellets, so I crushed them in a mortar with pestle into a powder.  I misted with water a Strophodonta from the Silica Shale with a spray bottle and sprinkled the powder on the shell.  The result after 5 hours is shown below.  This is going to save me a ton of time on a project on which I am working involving the need to clean hundreds of brachiopods...

 

[Lmshoemaker]

15 hours ago, Ludwigia said:

"This is certainly a good method which can bring excellent results as long as the fossil is completely calcified, silicified, or composed of any substance which the KOH won't dissolve. You have to watch out for gaps in the substance, otherwise you could be in for an unpleasant shock if you leave your fossil overnight. It's always best to check on the progression of dissolution every hour or so."

 

Yep. One thing I haven't worked with but would be wary of too is pyrite replaced fossils. It seems like this would be a very bad pairing. In response to your second comment, this is very true. This material can work its way under the pinnules of a crinoid and free them from the matrix, as an example.

13 hours ago, Doctor Mud said:

Thanks for sharing @Lmshoemaker very interesting. I hadn't considered alkali treatment for pre Quaternary fossils in consolidated sediments before.

 

I use KOH a lot to break down lake sediments - to defloculate the mud. The sediment can be bound together with organic material in various states of decomposition and the KOH dissolves it.

We also use NaOH to strip out contaminants from fossils prior to radiocarbon dating. Humic acids can percolate down in the sediment and make fossils appear too young.

 

i don't have any experience with KOH on fossils in rock, but a couple of things I've learned from using many chemicals from different types of sediment processing.

 

I always try to understand the chemistry of the reaction - how will this achieve what I want? What are potential problems? Different specimens can react quite differently so a test subject is always a good idea.

 

i wonder if putting the pellets on directly is the best approach? This would avoid having to use a solution if you want to avoid this but means you have no control over the concentration. This could be the cause of some adverse effects. Are you using a 90 % solution where a 10% will suffice? I usually use 10% on sediments.

 

 

I only use pellets because they are easier to control than a liquid. The concentration doesn't seem too important as I would imagine it would just control the rate of the reaction, which is pretty slow to begin with. Concentration might be worth considering, but for me I can't see it being something I'd want to work out personally.

[Lmshoemaker]

1 hour ago, Peat Burns said:

Thanks @Lmshoemaker for sharing this.  Tried it out this afternoon with promising results.  All I had around was KOH pellets, so I crushed them in a mortar with pestle into a powder.  I misted with water a Strophodonta from the Silica Shale with a spray bottle and sprinkled the powder on the shell.  The result after 5 hours is shown below.  This is going to save me a ton of time on a project on which I am working involving the need to clean hundreds of brachiopods...

 

 

Very nice to hear. This is on par with the results I am getting.

[taj]

Huh ? sold by Amazon .. Gonna test this on the spot  since I could not bring my KOH overseas...

[JohnJ]

I've also used KOH extensively on Texas Cretaceous specimens.  I've learned that pre-soaking specimens in water helps saturate interior cracks and voids that would destructively 'wick' the KOH inside. This will save you grief years in the future. It also provides the ambient moisture that helps the chemical react with the matrix. After treating a specimen, I will quickly soak and lightly brush with regular vinegar.  This is followed by a soak in water.  If any crystals form once the specimen is dry, I'll cycle through a couple more vinegar/water rinses.  The results can be remarkable.