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Stiff Pen Shell pearls (atrina rigida)

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  • Stiff Pen Shell pearls (atrina rigida)

    All of these came from a single stiff pen shell I found yesterday. All very small.
    The biggest one shown there is about 4.5mm. I'm curious if there's any value to them. If not, how big do they have to get to be of any value?

    Click image for larger version

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  • #2
    I buy pen pearls at 9/cts for small/baroque or misshapen, the price also depends on how many are chipped or cracked. If you do have any interest in selling the lot, please contact me I will be away next week for Tucson.

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    • #3
      Some of these are quite nice in size, shape and color.

      Pen pearls and shells tend to crack over time. These pearls will need to be dessicated slowly and with uniformity, because in a week or two they may start to break.

      While pens are considered nacreous pearls, they don't actually physically become highly nacreous until about year four or five.

      I presume you have the shell from which these came. Keep the shell near the pearls in a cool dry place away from the sun, but in a place you can hear spontaneous sounds coming from them. (I can hear mussel shells crack from across the room). Once the shell stops making sounds or quits peeling, your pearls now stand a better chance of surviving intact.

      I'd suggest holding on to these pearls for several months before marketing, afterall you might find yourself with a dissatisfied customer, especially if they invested a considerable amount of money for the pearls, metal and design.

      All that said, you are indeed lucky to enjoy such a rare find. Thank you for sharing them with us.

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      • #4
        prices for these pearls seems to vary a lot there was a small parcel of them on ebay not to long ago couple carats and went for 160 usd i bought quite cheap as well like 10 usd for some nice ones so there is no real set market price its a nice find in one shell !
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        • #5
          That is a very cool find, indeed. Dave is right about the potential for cracking. I hadn't heard the advice about listening for the shell's cracking noises -- that's terrific. My cats would go nuts!

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          • #6
            Originally posted by GemGeek View Post
            That is a very cool find, indeed. Dave is right about the potential for cracking. I hadn't heard the advice about listening for the shell's cracking noises -- that's terrific. My cats would go nuts!
            I have a big collection of shells with natural mabes, conjunctions, malformations, repaired cracks etc. I scrub the barnacles and other growth away, wash them well then set them in a basket to dry. In 3-4 days, you'll hear small clicks and ticks as the conchiolin dries and splits away from the shell. After about a week, you hear bigger sounds, like breaking terra cotta. If the shells themselves crack, they leave a razor edge so sharp, you could cut steak with them.

            Even though mussels and pens are a different order, their shells closely resemble each other. The main difference is in the pearls. Mussels are highly nacreous within the first year of growth and almost never crack. As I mentioned earlier, pen pearls are highly proteinaceous for several years and unfortunately many are found in an immature state.

            I'm quite certain, mature pen pearls can be every bit as high quality as a tahitian pearl though, once the nacreous structure forms over the prismatic layers.

            For that reason alone, farming pens for pearls is a difficult challenge.

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            • #7
              Thanks for all the great info. Fascinating stuff. I found another pen with assorted pearls.
              Click image for larger version

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              The biggest shown is translucent and soon after it started drying cracks began to appear and this morning they are quite pronounced.

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              • #8
                Great photograph! The cracking breaks the heart, though.

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                • #9
                  Originally posted by Gio View Post
                  The biggest shown is translucent and soon after it started drying cracks began to appear and this morning they are quite pronounced.
                  That's unfortunate, it looked like a nice pearl.

                  In the event you might encounter other specimens with those translucent pearls, there are a few treatments you may try.

                  Divide the transluscent from from the opaque. Blot them dry, fold them into a soft cloth and place them in jar or other non-metallic contain allow them to stand in cold, dry place for a few days.

                  Imagine if you will, how wood reacts when it's air or kiln dried. A slower, more controlled cure prevents cracking, while kilns can warp and crack wood severely.

                  Once the moisture content becomes lower, treat with polyethylene glycol. It's an inexpensive burn treatment available at any drug store, just be sure it's not otherwise medicated.

                  Achaeologists use the stuff all the time, expecially on artifacts recovered from shipwrecks, or even the salvaged wrecks themselves.

                  Conchiolin consists of polysaccharides and glycoproteins. The "poly" (even though it means many) will re-bind the sugars and the "glycol" will soften and even reconstruct the long-chains so they won't overly degrade in dry air. The "ethylene" part will act as the solvent to assist penetration and saturation.

                  You might be able to use automotive cooling system antifreeze (not window washer formulas) in the absence of anything else, but it often contains other additives like dyes and rust inhibitors.

                  I'm not suggesting it will work definitively on pen pearls, but you certainly have nothing to lose by trying.

                  I thiought about mineral oil as well, but I'm not certain if it will displace water sufficiently, without some rancidity.

                  Again, you're a lucky person! Finding natural pearls never gets old!
                  Last edited by Lagoon Island Pearls; 02-04-2013, 05:22 AM.

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                  • #10
                    Originally posted by Lagoon Island Pearls View Post
                    I have a big collection of shells with natural mabes, conjunctions, malformations, repaired cracks etc. I scrub the barnacles and other growth away, wash them well then set them in a basket to dry. In 3-4 days, you'll hear small clicks and ticks as the conchiolin dries and splits away from the shell. After about a week, you hear bigger sounds, like breaking terra cotta. If the shells themselves crack, they leave a razor edge so sharp, you could cut steak with them.

                    Even though mussels and pens are a different order, their shells closely resemble each other. The main difference is in the pearls. Mussels are highly nacreous within the first year of growth and almost never crack. As I mentioned earlier, pen pearls are highly proteinaceous for several years and unfortunately many are found in an immature state.

                    I'm quite certain, mature pen pearls can be every bit as high quality as a tahitian pearl though, once the nacreous structure forms over the prismatic layers.

                    For that reason alone, farming pens for pearls is a difficult challenge.
                    Hi Dave, excuse in advance my lack of knowledge but could it be possible by any chance that we are here referring to the periostracum instead of the conchiolin? The primastic layers has high flexibility while in the water and will crack when dried, is this what those pearls are made of? We refer to those as " Bundo " in Japanese.

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                    • #11
                      Originally posted by Cyril Roger Brossard View Post
                      could it be possible by any chance that we are here referring to the periostracum instead of the conchiolin?
                      Indeed, flexibility is the issue with this structure. While my hands-on experience with atrina is limited too (Modiolus m. has similar structure), it's my understanding this species does well to survive while attached or exposed to shifting cobble and other coarse substrate. As juveniles, clams like mud and mussels like structure, pens found a niche in between. Once a pen gets big enough and buried in sediments, they'll become nacreous, but even then it's over a protein rich prismatic layer which is still susceptible to cracking.

                      When shells dry, the first crackling sounds heard will be the conchiolin, afterall it's directly exposed to air and cracks much like old paint does. After a few days, once the moisture is drawn from the prismatic layers, the entire structure can crack. So yes Cyril we are discussing both in succession, I suppose.

                      I'm not sure how many pearl farmers heap in dry land middens anymore, but I'm sure any shell diver, oyster shucker etc. can recall shells crackling in the sun all day long.

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                      • #12
                        Originally posted by Lagoon Island Pearls View Post
                        Indeed, flexibility is the issue with this structure. While my hands-on experience with atrina is limited too (Modiolus m. has similar structure), it's my understanding this species does well to survive while attached or exposed to shifting cobble and other coarse substrate. As juveniles, clams like mud and mussels like structure, pens found a niche in between. Once a pen gets big enough and buried in sediments, they'll become nacreous, but even then it's over a protein rich prismatic layer which is still susceptible to cracking.

                        When shells dry, the first crackling sounds heard will be the conchiolin, afterall it's directly exposed to air and cracks much like old paint does. After a few days, once the moisture is drawn from the prismatic layers, the entire structure can crack. So yes Cyril we are discussing both in succession, I suppose.

                        I'm not sure how many pearl farmers heap in dry land middens anymore, but I'm sure any shell diver, oyster shucker etc. can recall shells crackling in the sun all day long.
                        We are indeed on the same page.
                        I do agree completely with the anecdote as I experienced it as well with Pinctada, now I am here referring to the periostracum loosing it's flexibility and density as the desiccation takes place.
                        I also experienced bundo pearls (made of prismatic layer) altered by the creation of cracks and/or fissure lines.
                        keeping such in moist environment did reduce the crack but as primastic layers goes, they do not have any stress strength.

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