Were To Use One Chemical Or Another

[MOROPUS]

I would like to know, if NaOH or HCl would be useful to clean fossils. I know they are dangerous, but the form I can easely found them, are always diluted.

I`ve never use them, but I have seen how HCl works on some corals...

Could you give me some advice on how to do it?

[MOROPUS]

By the way, the only chemical I have ever use was diluted Acetic acid (wine vinegar)!

[Harry Pristis]

There is no simple answer to this question, 'Moropus'.

A completely silicified fossil will not be affected by these chemicals. A calcified fossil will be devastated. The tricky part is knowing the composition of your fossil. You will have to make your own judgements about your own fossils.

[tracer]

if you type "hydroxide" in the search box here you will find all the references to using KOH (not NaOH) for echinoid prep. mr. woehr has described his process several times. strong bases are bad karma, as are strong acids. hcl, in my mind would be overpowered for most uses except perhaps careful use in a diluted form to remove carbonate matrix from silicified fossils.

if i used an acid or a base, i'd sure want to get it completely neutralized afterward.

i like air abrasion because i can control the process better.

[MOROPUS]

Corals in calcareous black shale????

[Infidel]

Why KOH rather than NaOH? I think the NaOH is easier to obtain retail, if it can't be substituted could you let me know why? Or is it just a strength issue, or perhaps because it isn't flaked?

[ashcraft]

Why KOH rather than NaOH? I think the NaOH is easier to obtain retail, if it can't be substituted could you let me know why? Or is it just a strength issue, or perhaps because it isn't flaked?

They both should work. Potassium hydroxide is also readily available, try looking at Draino. I believe they operate by binding with the cations (+ charged pieces) in the clay/rock, forcing them to break bonds that are holding the material together. I have been told that soaking heavy clays particularly in hydroxides will cause the clay to fall apart rapidly, allowing removal of fossils, or whatever else may be in it. Being basic, they shouldn't do much damage to carbonate fossils.

Brent Ashcraft

[jkfoam]

Corals in calcareous black shale????

Moropus,

Corals are composed of calcium carbonate. Hydrochloric acid will completely destroy calcium carbonate. Sodium hydroxide or potassium hydroxide would not have any effect on the shale or the coral so it would not help in removing the coral from the shale.

Moropus, a word about hydrochloric acid HCl). Hydrochloric acid is an aqueous solution of hydrogen chloride in water. So what happens when you take the top off a bottle of hydrochloric acid is that a small amount of the hydrogen chloride gas separates from the water as a gas and mixes in the air. Hydrogen chloride is a very corrosive gas and a toxic gas. You don't want to breath any of it. Any work with hydrochloric acid should be in a well ventillated hood. Also the hydrogen chloride gas will start attacking most all metals. If you place a bottle of concentrated hydrchloric acid on a steel shelf even with the cap tightened and well secure some of the hydrogen chloride will still escape and corrode the steel shelf. Hydrochloric acid is generally sold for swimming pool applications and cleaning rust stains. It is generally sold under the name Muratic acid at a concentratiion of 20 Baume (or 34-35 wt % in water). Thats about the most hydrogen chloride that can dissolve in water. If you don't have silicified fossils I don't recomend using Hydrochloric acid.

Sodium Hydroxide (NaOH) and Potassium Hydroxide (KOH). The dangers with these two materials are their corrisiveness and their toxicity. If memory serves me correctly they both have an LD50 of about 1mg/Kg. That means that that the lethal dose to 50% of test animals was 1 mg per 1 Kg body weight. About corrosiveness, I had a Chemistry Professor tell me that a boiling concentrated sodium hydroxide solution would dissolve anything. Now that may have been an exageration but I experienced it dissolving glass. Also it can cause chemical burns about as quickly as some acids. When you spill even dilute solutions of sodium hydroxide on your hands they feel slick like a soap solution. The reason they feel slick is because the sodium hydroxide has dissolved a very thin layer of skin!

From the fossil collectors point of view the big problem with these kinds of materials is how do you dispose of them when you are through with them. They are Hazardous Waste Materials and must be disposed of properly!

JKFoam

[Infidel]

Moropus,

Corals are composed of calcium carbonate. Hydrochloric acid will completely destroy calcium carbonate. Sodium hydroxide or potassium hydroxide would not have any effect on the shale or the coral so it would not help in removing the coral from the shale.

Moropus, a word about hydrochloric acid HCl). Hydrochloric acid is an aqueous solution of hydrogen chloride in water. So what happens when you take the top off a bottle of hydrochloric acid is that a small amount of the hydrogen chloride gas separates from the water as a gas and mixes in the air. Hydrogen chloride is a very corrosive gas and a toxic gas. You don't want to breath any of it. Any work with hydrochloric acid should be in a well ventillated hood. Also the hydrogen chloride gas will start attacking most all metals. If you place a bottle of concentrated hydrchloric acid on a steel shelf even with the cap tightened and well secure some of the hydrogen chloride will still escape and corrode the steel shelf. Hydrochloric acid is generally sold for swimming pool applications and cleaning rust stains. It is generally sold under the name Muratic acid at a concentratiion of 20 Baume (or 34-35 wt % in water). Thats about the most hydrogen chloride that can dissolve in water. If you don't have silicified fossils I don't recomend using Hydrochloric acid.

Sodium Hydroxide (NaOH) and Potassium Hydroxide (KOH). The dangers with these two materials are their corrisiveness and their toxicity. If memory serves me correctly they both have an LD50 of about 1mg/Kg. That means that that the lethal dose to 50% of test animals was 1 mg per 1 Kg body weight. About corrosiveness, I had a Chemistry Professor tell me that a boiling concentrated sodium hydroxide solution would dissolve anything. Now that may have been an exageration but I experienced it dissolving glass. Also it can cause chemical burns about as quickly as some acids. When you spill even dilute solutions of sodium hydroxide on your hands they feel slick like a soap solution. The reason they feel slick is because the sodium hydroxide has dissolved a very thin layer of skin!

From the fossil collectors point of view the big problem with these kinds of materials is how do you dispose of them when you are through with them. They are Hazardous Waste Materials and must be disposed of properly!

JKFoam

Likewise though, if your matrix is limestone based which is a carbonate, then the acids will dissolve that matrix, hence using the vinegar/HCL on them. Using caustic on limestone matrix is new to me but I'm anxious to try it. As for disposal, I think neutralizing with another acid or base, or just lots of dilution will take care of it. I tend not to use HCL anymore because I think it harms the fossil too much, and I didn't like all the holes I'd find in my jeans after the next wash . So I'll stick to vinegar for that.

Whereabout in Williamson County are you JK?

[jkfoam]

Infidel,

Disposing of HCl is much easier than NaOH or KOH. To neutralize HCl just add limestone rock to a container of HCl. The limestone will consume the HCl. Now NaOH and KOH are different. There you have to neutralize them with an acid (how do you know when you have added enough). Actually you should add an excess on HCl then neutralize the excess acid with limestone rock. If you don't know what you are doing or you are not a chemist then you are probably best to avoid the whole mess.

Infidel, I'm up here a little north of the hamlet of Walburg.

JKFoam

[Taxman56]

I used Muric Acids to try and brighten some weathered calcium based fossils from Mich. It really doesn't work that great and sooner or later it will start eating your fossil. I experimented once and just to see what happens and ate a 5 pound rock down to nothing. For a few days I had something I thought I liked and then it was GONE. LOL But I think it ate away some of the detail of the fossil while eating the bedrock at a faster rate.

[Placoderms]

MOROPUS,

This is what I have on the subject of chemical cleaners:

[Taxman56]

After reading several posts on this subject over the past year in the forum, I was wondering if anyone tried using muric acid or vinegar with some glass lab gear to set up a drip line on the fossil.

Submerging the fossil in acid will let the acid work on all sides, in and out eating off all the detail.

But if you think of acid rain that naturally etches the rock, the drops hit the rock quickly dripping down into and off the fossil, so the high points stick out and it slowly eats deeper in to the fossil and possibly weakening the acid so it doesn't eat to fast into the fossil.

It seems a good idea on paper anyway than just submerging the fossil. Which I like to do with junk fossils to see what happens.

Anyone have any luck trying to "brighten" up limestone corals such as those found in eastern Michigan. Their dark black but the corals weather out an off white. Acid just eats everything.

[siteseer]

I would like to know, if NaOH or HCl would be useful to clean fossils. I know they are dangerous, but the form I can easely found them, are always diluted.

I`ve never use them, but I have seen how HCl works on some corals...

Could you give me some advice on how to do it?

I have used HCL, it's commercial version, muriatic acid, for cleaning specimens of Dendraster gibbsi (Pliocene sand dollar). I diluted it with water to the point that allows me to touch it if necessary or by accident. A sand dollar will get eaten up but quick dips clean the edges of the plates, bringing more definition and contrast (more specimens with that black and white look). I worked with it outside. I haven't used it in years though, not wanting it around with kids coming over.