Robert Oster Plumb Nut ink bottle

Ink of the Week – Robert Oster Plumb Nut

John BosleyFountain Pen Ink 6 Comments

This week we’re going to take a look at Robert Oster Plumb Nut. I originally put this ink on my want list after seeing it in a few different posts on Instagram and thinking to myself, “that’s a pretty great color”. I’m sad to say that when I did finally get a bottle for myself, I think I only used it once. I just wasn’t as impressed with it as I was when I saw it in photos. How about I give it a second chance and find out if maybe we just got off on the wrong foot.

Robert Oster Plumb Nut

To start, let’s take a look at the ink itself. It’s a dark, dusty pink color. Imagine a much darker version of PenBBS Rose Quartz. You might even call it purple if you really wanted to. I can see the resemblance to the skin of a plum.

Robert Oster Plumb Nut ink color

Wondering if plum is spelled “plumb” in Australia, I did a few Google searches. I couldn’t find any reference to the fruit being spelled “plumb”. That word has completely different meanings, such as “to measure the depth” and “to test for being vertical”. Still, I’m going to assume the name of this ink is referring to the fruit and not depth or verticality.

This ink shades fairly heavily when not used in super-wet nibs. In wet nibs, it looks a lot darker and doesn’t show as much shading. It doesn’t have any sheen, but with heavy applications does show darker banding that almost looks like sheen.

I was disappointed to discover that this ink does not have an interesting chromatography like the ink I used last week. With water, it only spreads out into a lighter shade of pink with no additional colors. It is not very waterproof.

Robert Oster Plumb Nut ink review chromatography

This ink does not have an interesting chromatography.

Robert Oster Plumb Nut ink review waterproof

This ink is not very waterproof.

This ink has pretty good dry times. I felt like it was generally dry shortly after writing with it and I didn’t really have to wait to turn the page while writing in a journal. Another plus is that this ink doesn’t seem to smear once dry. I didn’t see any smearing during my writing or doodling sessions.

The Pens I Used

Each week I choose five different pens to fill with the ink I’m testing. My goal is to get a variety of nib sizes and styles, as well as a mix of modern and vintage pens. Here are the pens I chose this week and some writing samples from each:

Robert Oster Plumb Nut ink pens used

Pens used this week (L-R): Esterbrook SJ, Parker Challenger, Pelikan M200, Pilot Metropolitan, Pelikan M800

Robert Oster Plumb Nut ink nibs used

Here’s a peek at the nibs (L-R): Esterbrook SJ, Parker Challenger, Pelikan M200, Pilot Metropolitan, Pelikan M800

Esterbrook SJ (vintage) – 9550 EF nib

Easily my least favorite combination of the week. This extra fine Esterbrook nib just doesn’t bring out any of the qualities of this ink I want to see. There is no shading and it’s much too light for my preference.

Robert Oster Plumb Nut ink ef nib

Writing sample with EF Esterbrook nib

Parker Challenger (vintage) – flex M nib

This combination looks a lot better. The Parker nib brings out some shading in the ink that wasn’t there with the extra-fine nib. It also makes the ink look darker.

Robert Oster Plumb Nut ink vintage flex nib

Writing sample with vintage M flex Parker Challenger nib

Pelikan M200 – M nib

This is more my preference for this ink. The Pelikan nib writes wetter and gives a bit less shading, which I actually prefer with this ink. I think maybe since it’s a lighter ink, I just want it to look darker and this nib gives me that.

Robert Oster Plumb Nut ink Pelikan M200 nib

Writing sample with M Pelikan M200 nib

Pilot Metropolitan – M nib

It’s funny how different inks can change your impression of a pen. When I used this Metropolitan with the Yama-budo, I thought it was a great combination. With this ink, the Metropolitan nib feels a little dry and makes the ink look unimpressive.

Robert Oster Plumb Nut ink Pilot M nib

Writing sample with M Pilot Metropolitan nib

Pelikan 800 – custom grind B nib

This is what I wanted out of this ink. This wet Pelikan nib makes it look dark and dusty with very little shading. In my opinion this ink wants a very wet nib and this is just the nib to make it look great.

Robert Oster Plumb Nut ink pelikan B nib

Writing sample with B Pelikan M800 nib


On cheap paper, this ink did tend to bleed with the wetter nibs. On fountain-pen-friendly paper, I didn’t observe any bleedthrough or feathering, even with the flex nib. Unless you plan to use nibs that aren’t very wet, stick to good paper with this ink.

Robert Oster Plumb Nut ink clairefontaine paper

Writing samples on Clairefontaine Basic paper

Robert Oster Plumb Nut ink Life Noble paper

Writing samples on Life Noble paper

Robert Oster Plumb Nut ink leuchtturm paper

Writing samples on Leuchtturm paper

Cleaning The Ink Out Of Pens

As I’ve said in the past, red inks are typically more difficult to clean out of fountain pens. I think this one has a low enough saturation that it’s fairly easy to clean. It came out of all pens this week pretty easily. I wouldn’t hesitate to use it in any of the pens I own.


While Robert Oster Plumb Nut may not have been exactly what I wanted, I am happy to say that I’ve found enjoyment in using it. When used with a wet nib, this ink writes nice and dark with little shading. This makes it much more exciting (to me) than when I use it with a dry or fine nib. I would have liked for it to have an interesting chromatography, but that’s not the case. I found that I enjoyed using it more for doodling than I did for writing. Maybe that’s why I didn’t like it so much the first time I tried it. It might have just been used in the wrong pen and only used for writing. I’m not going to say that I love this ink, but I will say that I’m glad to have discovered that, when used in the right pen, I at least enjoy using it.

Robert Oster Plumb Nut ink doodles

Comments 6

  1. This ink seems to have a slight identity crisis. It doesn’t know what it wants to be when it grows up! 🤣 An ‘in between’ kind of color to me. Thanks for the pen nib photo. Always interesting to see the differences.

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  2. Agree with the above commenter, but, alas, “in between” colors are my favorites. Looks like another I *have to* buy. John, your blog is beginning to be troublesome for me. 😉

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  3. I wonder if the “plumb” is reference to lead, to the leaden tone of the ink? I kind of like the way it looks with the Parker and the Pelikan, but I don’t know that I would use it. There are just too many other inks I like better.

    As always, I love your illustrative doodles.

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