Penetralia ~ Fountain pen Ink review ~ Diamine Shimmertastic Firefly

Right: Clairfontaine paper. Left: crappy 90gsm copy paper

Now this is a Fantastic, Shimmertastic ink! As advertised…

This is my first ink review and I have to say I love this ink! I got this ink as part of my first batch of purchases, alongside my Pilot 74 and Leonardo Furore and I’m so glad I did. I was looking for a distinct colour option that would pop when I sign prescriptions, which are on green paper. So, what’s opposite green on the colour wheel? Red.

I was looking through many red options and then suddenly came across other features inks could have (like shimmer and shading etc) and immediately decided I wanted to sign prescriptions in a shimmer ink!

I don’t know how legal using non-permanent, non-blue or non-black ink is on prescriptions, but so far, no one has complained. I’ve been using about 15 different inks over the last 8months so it’s time to write a review.

Firstly let take a closer look at the ink on nice Clairefontaine paper:

It’s glaringly obvious, even in the dark, that this is a shimmering ink! It’s fantastic! This ink is mostly red, but with a powerful orangey twang to it. You can see at the edges of the swatch, where I didn’t fully go over with each pass, it’s more orange than red. I did my swatch, half with 3 passes (near the top) and half with 2 passes (near the bottom) and the depth change in the colour isn’t dramatic on “nice” paper — which is what I want. You can see however, the pooling of ink leaves distinct darker shades where my brushing lifted off the page.

The “nicer” paper really shows up the darks around the edges, which I didn’t see much of on “crappy” copy paper. Also with the Benu the shimmer is great. No complaints at all. I think the Benu is a wetter Broad than the Leonardo, hence more shimmer in the Benu, despite them both being broads. It definitely took longer to dry on the “nicer” paper. Even with the Pilot 74 fine nib, the shimmer is there, you just have to look more closely for it.

There’s no feathering, no show through (except with very heavy ink drops on the page), no ghosting, nothing — just a well behaved ink on nice paper.

Now lets get a close up on “crappy” 90gsm copy paper:

In all honesty, a solid performance on “crap” paper too! With the swatch there’s a definite increase to the depth of the colour with each pass, but even with my Pilot74 fine nib the shimmer is obvious. The Benu takes the show again. The ink definitely dries faster on the crappy paper, which is good for my office use and the lines are consistent with no hard starting or ruining my pens for either paper.

I found the ink was really easy to clean out of my pens too. I did use the ink in my Parker Jotter fountain pen too (my starter of all starter pens) and I loved it in their too, easy to clean.

I don’t know, you could even argue that the shimmer is brighter on crappy paper. no dark edges though, but you may not want the shading bit of the ink. There’s a little bit of bleeding through with the wet Benu writer, and all the ink droplets bleed straight through to the other side of the page with a brilliant full red colour. Otherwise a well behaved ink, even on crap paper.


I finally got a chance to play with my chromatography paper, after it took a million years to get to me (thanks COVID!) But I’m so glad I’ve got it. Isn’t this just the greatest technique!? Firefly, being my first chromatography test did not disappoint. you can see the gold specks get left behind very early on, and there seems to be 2 weights of red/pink in this ink too — there’s a small inner pick then a gap then the next red starts. On the outside the lightest yellow colour. Really enjoyed this!

Why is this ink in my collection?

I think this ink is fantastic! I love the colour and it behaves really nicely, even on my crappy prescription pad paper. Is definitely adds a little flare to my day. Its super easy to clean, didn’t clog up any of my pens and it’s one I’m going to keep using

Is this a ink fit for a GP?

100% As long as your legal department doesn’t loose their marbles, but I think that’s going to be the case with literally any non-permanent, non-blue, non-black ink one brings to work. It’s definitely a staple in my daily practice and I shall protest e-prescribing until the end of time for this reason! ;-P

Thanks so much for reading and remember no matter who you are, “first, do no harm.”




An Australian GP with a love for fountain pens, writing, gaming and gardening, throwing in an occasional rant along the way!

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An Australian GP with a love for fountain pens, writing, gaming and gardening, throwing in an occasional rant along the way!

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