Monteverde Gemstone Onyx Ink Bottle, Black - 30ml

The Onyx ink is part of the Monteverde Gemstone collection — a series of fountain?pen inks inspired by the hues and richness of gemstones. According to a review:

“Onyx is a classic black ink.” 
Although the product page itself is less explicit about the “gemstone inspiration” for this particular shade, the collection framing implies the notion of a refined, rich black rather than a basic or plain black.

While many black inks aim simply for neutrality and legibility, Onyx positions itself as a premium black with depth, subtle character, and the benefit of Monteverde’s performance?enhancing ink formula (see below). The 30?ml glass bottle is typical for this collection and gives the ink a collectible and stationery?desk friendly appeal.

One of the key selling points of this ink lies in Monteverde’s proprietary “Ink Treatment Formula (ITF)”. From the review cited:

• The review mentions it behaves well and is suited for fountain?pen use.
  Though not explicitly given on the product description of Onyx, Monteverde generally states for their ink lines:

“Enjoy peak performance with ITF which drastically improves ink?flow quality, extends cap?off time, lubricates and protects the ink feeding system from corrosion or clogging.”
In practice this means:

• Better flow in the fountain pen (less skipping/hard starts)

• Potentially longer time between caps being removed and nib drying out (though you should still recap)

• Additional protection for your pen’s feed system (important if you switch inks often or let a pen sit)

Thus, Onyx isn’t just about the colour — it is engineered for reliable fountain?pen performance.

Colour impression:

• In the review by Mountain?of?Ink, Onyx is described as “a classic black ink.”

• Swabs on high?quality paper (Tomoe?River) reveal “some black sheen” — meaning though it appears black, there is slight reflective quality under certain lighting.

• In writing tests: on Rhodia, Tomoe?River and Leuchtturm notebook papers, the ink showed no feathering, moderate show?through, no bleeding; on cheap 20?lb copy paper there was some feathering and a few dots of bleeding.

Writing behaviour & technical specs:

• Dry time: ~20?seconds on good paper (Rhodia/Tomoe?River) as per the review.

• Water resistance: Review indicates “Medium” water resistance. 

• Performance was described as “average flow” in a flex nib pen (vintage Mabie Todd Swan) but overall good enough for everyday use.

Summary of behaviour: If used on decent paper and with a properly tuned pen, Onyx offers a dense, rich black that reads as classic and professional but with a slight hint of subtle character (the sheen). On lower?quality papers the performance holds up reasonably but you may notice more show?through or minor feathering.

• Professional & versatile colour: If you need a black ink that is reliable for everyday use (notes, correspondence, signatures) yet with a little enhanced finish (sheen, rich saturation) rather than a flat generic black, Onyx delivers.

• Performance?oriented formula: The ITF treatment adds confidence in flow, pen compatibility and durability — especially useful if you have pens that see infrequent use or you swap inks.

• Bottle & value: The 30?ml glass bottle is manageable, elegant, and suitable for regular users without going overboard.

• Collectible and aesthetic appeal: Within the Gemstone line, Onyx sits alongside other gem?inspired colours — so for ink enthusiasts it holds thematic interest beyond mere utility.

Things to Consider / Limitations

• Paper and nib matter: While the review shows good performance on high?quality paper, on very cheap or absorbent paper you may see more show?through or bleed. The review noted some feathering on 20?lb copy paper.

• Sheen is subtle: The “small black sheen” is noted only in large swabs on premium paper. If you expect high sheen or dramatic visual effects, you may find Onyx more conservative.

• Water?resistance is moderate: Although described as “medium” in one review, this is not a strongly waterproof or archival ink. If you’re writing documents needing heavy water resistance, consider that caveat.

• Quality?control concerns in general: In the broader fountain?pen community there are documented issues with some Monteverde ink bottles (mould, odd smells, contamination) — while not specific to Onyx alone, it is wise to purchase from a reliable retailer, inspect the bottle on opening, and use good storage practices.