There's a room packed floor to ceiling with tiny hand-labelled cardboard boxes which contain the moulds for every piece they've ever created.
There's a room where a row of blue coat-wearing craftspeople polish rings to a high lustre, and a room where blazing blowtorches melt down and mould precious metals.
Finally, there's a room for fine work and finishings, where a waterfall of Karen Walker chains wait to be strung with pendants, a cluster of the designer's signature silver acorn caps rest on a wooden bench awaiting their acorns, and a pair of white gold pansy rings are ready for the delicate placement of pavé diamonds, which rest dazzlingly beside them in a shallow dish.
It is these diamonds I'm here to look at, as they belong to the newly released Karen Walker Diamond collection.
"We've been asked for engagement pieces for years," Walker tells me. "So we decided to create a diamond range that would allow people to celebrate and mark anything from engagements to anniversaries to special treats."
There are close to 30 individual ring styles in the collection, made up of three separate stories.
"The Solitaires have a classic engagement ring starting point, but with our twist," explains Walker. Working across three principal diamond cuts - brilliant, pear and princess - each features chic signature daisy cutouts that allow light to penetrate the sparkling stones, which come in a variety of carats and sizes.
In a nod to the most recent fine jewellery additions, the Diamond Botanicals celebrate posies of wild wax flowers, cradling diamonds at their centres, and "are more of a style piece that can be worn every day. They're pretty, delicate and will look good with jeans and a sweater, or an evening gown," Walker says. "The Pansy story consists of the 'look at me' pieces, but again, in true KW style, we like the idea of contrasting these very eye-catching pieces - the largest triple pansy ring has more than 300 diamonds in the setting - against denim and a T-shirt, right through to cocktail or evening."
There is an air of intense concentration in this thriving workshop, as all around us the talented staff focus on their individual and precise skills.
"There are still a few others [jewellery workshops] like this, but probably not of the same size," the managing director John tells me. The company has been in its current digs for about 45 years, and I suspect some of the original tools and machinery remain. As do the staff. Dave, the factory manager, who's kind enough to show me what $46,000 worth of white gold looks like pre and post-melting, tells me he's been with the company for many years.
John came into the family business after his father, who still works here, and both of John's sons have also joined the team, one "on the bench" as a jeweller and second-in-charge to Dave, the other in IT, sales and marketing.
As well as creating all Karen Walker's fine jewellery, the company supplies jewellers across the country and beyond. They're also busy crafting intricate sword, axe and key pendants and solid sterling silver rings for the cinematic release of The Hobbit, having held the licence to manufacture Lord of the Rings jewellery since the release of the first film back in 2001. And according to John, "it is still very, very popular. The One Ring and the Evenstar pendant are the top sellers."
Though some of the jewellery is outsourced for manufacture - in other New Zealand locations as well as China and Europe depending on demand - the One Ring, and a variety of Karen Walker's collections, are always produced locally.
I ask John to talk me through the processes that go into creating each of these exquisite pieces. "The original pattern is hand-crafted from Karen's drawings.
"From there we individually manufacture each piece, working from the jewellers' benches to the setters who secure the stones, to the polishers who add lustre to the product.
"The items are then quality-controlled up to a high standard before leaving the factory. Each ring can go through up to seven people, depending on the design."
"All the rings in the Karen Walker Diamond collection are available in yellow or white gold, palladium or platinum, with platinum being the most expensive of the metals due to its relative scarcity. Because of its hardness it's also the most difficult to work with."
Of her luminous new range, Walker says, "Obviously I like them all, but the ones I'm wearing most right now are the triple pansy pavé and the small Botanicals."
Her favourite cut is the princess, and yellow gold is her favourite metal, "but if it's next to diamonds, white gold".
And of the diamonds themselves, "It's the perfection of it that's fascinating."
