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Thread: Decreasing Surface Tension in Silicone Sacs?

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    Default Decreasing Surface Tension in Silicone Sacs?





    I currently have this Wahl LF fitted with a #15 Silicone sac, and the main annoyance I noticed is that the surface tension of the sac loves to hold a fair bit of ink up near the grip. As a result even storing overnight upright will burp upwards into the cap, especially in shirt-pocket transit due to the bit of air pocket behind the ink and doesn't just drop down to the bottom of the sac.



    Wondering if maybe there is some kind of agitation method I can put into the sac that will still be lever friendly to the sac itself without blocking the feed.



    Though I do have some #18 silicone sacs ordered, hoping that the sac diameter will help cut down on the surface tension. The inner barrel diameter is 0.31" (which could barely fit a #20 sac, so a #18 should be fine with the pressure bar taken into consideration).



    I'm curious if there are other methods in regards to the surface tension (though I imagine using different ink is one of them).

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    Default Re: Decreasing Surface Tension in Silicone Sacs?

    what if something was added into the sac before it gets sealed onto the pen?
    The way some converters have an agitator in them or the way a platinum cartridge has that steel ball as an agitator?

    maybe some tiny plastic pellets? preferably something that does not interact with ink obviously.

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    Useless mhosea's Avatar
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    Default Re: Decreasing Surface Tension in Silicone Sacs?

    I tried a few things, but the only one I can remember was a strip of polypropylene plastic cut from one of those ubiquitous reusable food storage containers. I sanded the edges so that it couldn't perforate anything. It could move a little along the sac, so that was a sort of agitation, but also ink might wick along it. I wish I could remember more about how much it helped, or not, but the other aggravation with silicone sacks is gas permeability, and I could think of nothing to ameliorate that problem.
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    Default Re: Decreasing Surface Tension in Silicone Sacs?

    Just out of curiosity, why the silicone sacs?

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    Default Re: Decreasing Surface Tension in Silicone Sacs?

    Quote Originally Posted by dneal View Post
    Just out of curiosity, why the silicone sacs?
    Because latex sacs are harmed and ruptured by Alkaline ink (which includes all of Iroshizuku), the gold nib and celluloid or ebonite grips/feed would be fine with that. Also because silicone won't further attack the celluloid when it ages, makes the barrel translucent.

    And not PVC because it would attack the celluloid. I've installed PVC into a Pilot Super 250, Parker Slimfold, and my Sheaffer Snorkel Valiant 1st year (with the 14K solid gold snorkel tube) and those work well. Same general ink-related reasoning for their usage as well.

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    Default Re: Decreasing Surface Tension in Silicone Sacs?

    Ok, just seems more trouble than it’s worth - to me anyway.

    I would think a sac with a larger diameter would be more likely to resist problems with surface tension (which is where you appear to be going). More liquid means more weight, and a larger diameter means more area that has to maintain surface tension; but it’s still a minuscule difference.

    Do other inks have this problem as well? Private Reserve, for example, will “stick” in a cartridge - one of the few inks I’ve found to do this.

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    Useless mhosea's Avatar
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    Default Re: Decreasing Surface Tension in Silicone Sacs?

    Quote Originally Posted by dneal View Post
    Do other inks have this problem as well? Private Reserve, for example, will “stick” in a cartridge - one of the few inks I’ve found to do this.
    I don't think it's specific to any particular inks, rather to the silicone sac material. In other sacs surface tension is not an issue because the ink touching the sac material slides along it under gravity. With silicone, the ink touching the silicone just seems to stay put. I tried to use silicone sacs in Snorkels when they first came out because it's such a pain to change the sac in a Snorkel. The idea was "once and for all" sort of thing, also to allow the use of any ink. It's not that I can confirm or endorse the lore about ink choices and latex sacs, but a failed sac in a Snorkel tends to be a real mess and to cause rusting of the metal parts, so better safe than sorry. Unfortunately, the gas permeability and surface tension issues made silicone a miserable sac material in Snorkels for me. If there was an ink choice that worked particularly well, I never noticed it. Within a year, I had changed all of them out to PVC sacs from Woodbin. PVC is the perfect choice for Snorkels IMHO, since the PVC sac is shrouded in metal. You give up a little ink capacity but in exchange you don't have to worry about anything. Too bad nobody else has stepped up to commission the manufacture of more PVC sacs.

    If Karl's pen were black celluloid or hard rubber, I would use latex with any ink and just change it when it needed it. In fact, I do precisely that with a Sheaffer OS balance. I changed the sac earlier than it probably should have needed it, after only a few years, since it seemed to stick to itself and generally be less resilient, so there might be something going on there. I just don't happen to mind or care. However, I would choose silicone on Karl's actual pen for no other reason than to prevent further darkening of the barrel due to latex out gassing.
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    Default Re: Decreasing Surface Tension in Silicone Sacs?

    [QUOTE=mhosea;289215]
    Quote Originally Posted by dneal View Post
    If Karl's pen were black celluloid or hard rubber, I would use latex with any ink and just change it when it needed it. In fact, I do precisely that with a Sheaffer OS balance. I changed the sac earlier than it probably should have needed it, after only a few years, since it seemed to stick to itself and generally be less resilient, so there might be something going on there. I just don't happen to mind or care. However, I would choose silicone on Karl's actual pen for no other reason than to prevent further darkening of the barrel due to latex out gassing.
    My only hang up would be not using the ink of my choice with it due to being a latex sac, but there's so many other inks I could use that are fine.

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    Default Re: Decreasing Surface Tension in Silicone Sacs?

    Installed a #18 sized, which was rather snug in the barrel (liberally talc'd to slip it down). Last two days now it has not burped into the cap, and shining a light thru thru the, it seems easy to tap it a few times and the ink drops.



    Even without dropping the ink down before sitting it upright in a cup (around 60 degree angle), it doesn't seem to push any ink up, almost as if the diameter was enough for the air to break the tension when it does expand. Also as a test I wrapped the barrel with my hand to warm up the whole thing upright and watched the nib/feed without any adverse effect. The sac is mostly full presently (since there's just enough surface tension that if you knock the ink to the bottom, you can dip it again and push out the air on the top to fill some more).

    So , so far good results. The next test is to actually travel between locations with it rather than just sit on a desk in controlled temperature.

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    Default Re: Decreasing Surface Tension in Silicone Sacs?

    My Parker 21 holds ink at the top of the sac. Funny how was get concerned about matters that make no difference in pen function. The black sacs probably do the same, but I can see inside. Out of sight, out of mind...LOL!!

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    Default Re: Decreasing Surface Tension in Silicone Sacs?

    Quote Originally Posted by Chuck Naill View Post
    My Parker 21 holds ink at the top of the sac. Funny how was get concerned about matters that make no difference in pen function. The black sacs probably do the same, but I can see inside. Out of sight, out of mind...LOL!!
    They might 'hold' ink in a particular spot, but I'm guessing you didn't read too much into it because otherwise you would know that latex sacs don't cause further problems because they don't suffer gas permeability. With silicone sac, the large air pocket can grow further because the wall of the silicone sac is very gas permeable (air and vapors travel easily thru it), as a result, unlike a latex sac doing the same thing (holding ink in places) the ink gets all pushed up into the cap even upright.

    BUT.... latex sacs don't do this, as it's already been known that ink just slides around the surface of latex sacs, it's not just a visual observation, but something known by those before us.

    Plus the sac in your Parker 21 , like the 51 Aero, are not Silicone, they're PVC ("Pli-Glass"), they don't suffer the gas permeability of silicone sacs.

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