Cleaning Paua Shells
Printed From: The Fishing Website
Category: Diving
Forum Name: Spearo's Corner
Forum Description: Free-divers & spearos chat about their sport
URL: https://www.fishing.net.nz/forum/forum_posts.asp?TID=35091
Printed Date: 10 Jun 2026 at 12:19am
Topic: Cleaning Paua Shells
Posted By: kolt45
Subject: Cleaning Paua Shells
Date Posted: 30 Nov 2008 at 8:00pm
After my first go at cleaning paua shells, I got mixed results. Using H2SO4, I dunked the shells for a few minutes, then used a wire brush to clean off the outer shell. Most have a pretty bland outside, but decent colors inside. One turned out fantastic on the outside, but sun damage basically ruined the inside. Does anyone know of a way to restore the color or is it too late?   |
Replies:
Posted By: long john
Date Posted: 30 Nov 2008 at 8:28pm
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try using sulphuric acid next time ------------- Proud member of the Glen Innes Spearfishing Club |
Posted By: Hairy Little Dwarf
Date Posted: 30 Nov 2008 at 8:31pm
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I've had good results with Oil of Vitriol ...And I think the sun damage is a one-way process unfortunately. ------------- The Dreaded Shark-Eating Man! |
Posted By: kolt45
Date Posted: 30 Nov 2008 at 8:39pm
sulfuric acid = H2SO4  HLD, I've read about mineral oil being the ticket to keeping the shine, will have to get some. Bummer about the sun damage. Looks like I've just got to go get some more  . |
long john wrote:Posted By: Mullins
Date Posted: 30 Nov 2008 at 9:15pm
| I think he meant Hydrogen Sulfate, does a much better job |
Posted By: kuuni
Date Posted: 30 Nov 2008 at 9:17pm
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Get one with a nice inside and then just stick the outside on a buffer wheel/grinder for a bit
BTW, I think LJ gotcha kolt :P |
Posted By: Paul G
Date Posted: 30 Nov 2008 at 9:30pm
| Don't breathe that dust Kuuni |
Posted By: Minksta
Date Posted: 01 Dec 2008 at 6:35am
| Yeah what kuuni said kolt, then a bit of really fine wet and dry sandpaper to get a nice finish! |
Posted By: kolt45
Date Posted: 01 Dec 2008 at 7:29am
Is that how they do the ones in the airport shops? and yes, I think you're right - the Dwarf's "oil of vitriol" too. Maybe I should try spirits of salts next time?  |
Posted By: Nick W
Date Posted: 01 Dec 2008 at 10:42am
| Angle grinder. Dont breath in the dust tho. can show you some on wednesday at the meeting if you want. |
Posted By: kolt45
Date Posted: 01 Dec 2008 at 11:39am
| Yeah, definitely bring some in. |
Posted By: long john
Date Posted: 01 Dec 2008 at 8:58pm
I try....  ------------- Proud member of the Glen Innes Spearfishing Club |
Posted By: kolt45
Date Posted: 01 Dec 2008 at 9:06pm
Let's all pick on the American guy  . Don't let all those H+ ions get to your head - they tend to dissolve rocks! I guess I'm going to stick with my oil of the philosopher's stone and leave the lung-tissue-damaging, dust breathing up to all you other fellers. |
Posted By: long john
Date Posted: 02 Dec 2008 at 10:44am
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If you gring them wet you'll avoid the dread silicosis. Alas, you don't get that structured surface look that yours have. ------------- Proud member of the Glen Innes Spearfishing Club |
Posted By: kolt45
Date Posted: 02 Dec 2008 at 11:27am
| Maybe an acid bath, followed by a wire wheel spin is a good way to go. Thoughts? |
Posted By: ethan18724
Date Posted: 22 Feb 2015 at 12:25pm
Just get the shell, and put it in a ice cream container with milk, and leave it for 2 weeks. the curdling process of the milk reacts with the outer calcium which breaks it down. after the shell is taken out. just wipe the inside of it with a sponge an ajax. this worked well for me.  |
Posted By: snatch77
Date Posted: 22 Feb 2015 at 8:17pm
 milk!? really? |
Posted By: Diver Dan
Date Posted: 22 Feb 2015 at 8:55pm
I have to try this!!!! ------------- Proud member of the Glen Innes Spearfishing Club |
Posted By: S.H.A.G
Date Posted: 23 Feb 2015 at 9:19am
Trying this tonight! ------------- Spearos Hunters And Gatherers |
Posted By: Troy Tempest
Date Posted: 07 Mar 2015 at 3:54pm
So, I gave the old milky paua trick a go and got some mixed results. Two weeks on and here is the best of them. The outsides have little change, but the inside has come up nice. ------------- ·.¸¸.·´¯'·.¸¸·´¯'·.¸¸.·´¯'·.¸ ><((((º> .¸¸·´¯'·.¸¸.·´¯'·.¸ ><((((º> Just quietly getting on with it... |
Posted By: Steps
Date Posted: 08 Mar 2015 at 9:36am
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Paua shell is basically different forms of calcium and other minerals. Calcium varies in appearance from a seashell, cement, concrete, plaster of paris, teeth, enamel toilet..garden line, wall board , the hard water line around a spa/ swimming pool. your bones. Cacuim is eaten by acid... battery acid H2SO4, oil vitriol, sulphuric acid are all the same thing but can be at different concentrations. The type and concentration of the acid, length of time, determines how fast the calcium is eaten into. The white outside is a form that is eaten faster than the pretty part... There are other acids also mild like lactic acid.. in milk, acetic acid in vinegar, citric acid in citrus fruit and the packet in the spice cupboard, toilet bowl cleaner (hydrochloric acid) All will do the same thing to a shell, at different concentrations, over time frames. Once the shell is stripped of the white deposits, a buff up on a buffing pad on the bench grinder, with a fine cutting rouge.. then a fine seal coat of a clear lacquer The bench grinder wire wheel and dust mask is by far the best to clean off, and a buff with a pad and rouge to finish... The down side to this method is the outside often has had some sort of tunnelling 'bug' going thru and to get these out the shell can get rather thin in places. Where as the acid method cleans out these imperfections better leaving a well presented but 'contoured' outside surface. I have a whole box of shells was experimenting with a few yrs back for lures and 'eyes' on luminescent painted stray line sinkers. |
Posted By: Dobo
Date Posted: 10 Mar 2015 at 11:51pm
| Anyone tried caustic soda mixed with hydrogen peroxide? Exothermic reaction seems to clean most things extremely well.... |
Posted By: Steps
Date Posted: 11 Mar 2015 at 8:57am
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Hmmm....never tried that , thread, with caution, my chemistry off the of my head says that has potential to maybe get a little 'hairy'... from the reaction one could get depending on the concentrations of the chemicals...maybe the order of which u mix one into the other and gases given off.... Strongly suggest do a lot of homework before going down that route.... |
Posted By: loviz
Date Posted: 18 Mar 2015 at 7:59pm
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I have been playing around a bit too. Seems like its a bit lucky dip as to how the shell looks under al the white calcium barnacle stuff. I had a play around with some very strong nitric acid which I had to dilute back to make it possible to even work with, the nitric ate the shell as well as the nice rainbow bit and the shell went paper thin over a couple of hours. So a strong acid is not necessarily the best, as the coating on the shells is not even its might be a case of getting the balance between eating the outside adequately and how much the inside is eaten. I also have been palying with the much more mild citric acid (same as you would get in the supermarket mixed about 1:1 water) and with some lactic acid from rotten milk. the milk is the slowest, citric works well and most of the barnacle can be scrubbed off within a few hours, a second soak seems to get the rest and you are dealing with fairly safe chemicals by comparison. |
Posted By: long john
Date Posted: 18 Mar 2015 at 8:00pm
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Any chance of pics? ------------- Proud member of the Glen Innes Spearfishing Club |
Posted By: McKoy
Date Posted: 18 Mar 2015 at 8:15pm
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What I've always done is grind away the shell using a wirebrush on a grinder wheel. To make shiny ashtrays I've just used gun oil of all things. Acids are going to eat the hell out of your calcium carbonate shell, in saying that, the best ashtrays have the deposits left intact for heat resistance. |
Posted By: Diver9888
Date Posted: 18 Mar 2015 at 9:47pm
I sure hope it works as my two weeks is also up. My shed stunk after two days (I couldn't leave it out side as my dog would drink it) and the container is full of live maggots right now. ------------- Do it today because tomorrow has a habit of not turning out the way you want |
Posted By: spearfisher916
Date Posted: 18 Mar 2015 at 10:39pm
Maybe the lid could go on the container?
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