WHAT IS OVERDYEING?
When browsing the Iron Heart website, you’ll notice that many of our jeans, shirts, and denim jackets are available in both “indigo” and “indigo-overdyed-black” versions — but what does this mean?
Yarn Dyeing vs. Overdyeing
At Iron Heart, we use two main techniques to colour our fabrics — yarn dyeing and overdyeing. The first involves applying dye to the yarns before weaving the fabric. For example, our traditional indigo denim is woven using indigo rope-dyed warp yarns and white or natural weft yarns.
Overdyeing, on the other hand, refers to applying dye after the fabric has been woven and the garment constructed. In many cases, this involves adding a secondary dye to fabric that has already been yarn-dyed. For our “indigo-overdyed black” denim, we take a standard indigo garment and dye it a second time — this time in black dye.
Why Overdye?
“…But if you want black jeans, why not just weave denim with black yarns?” If that’s what you’re thinking, the answer is simple — we do that too. The difference between our yarn-dyed and overdyed black denim, however, is very noticeable.
In the textiles industry, overdyeing isn’t typically used as a primary dyeing method. Instead, it’s a technique employed to add character to fabrics, producing a deeper or more nuanced shade. While our yarn-dyed black denim offers a very even, jet-black appearance, our indigo-overdyed-black denim displays an entirely different character.
Because the secondary dye doesn’t penetrate the fibres as deeply, the result is a unique middle ground — no longer indigo, but not quite black. As the dye fades through wear and washing, more of the original indigo yarns are gradually exposed, which then fade in the classic indigo way. This means that while yarn-dyed black denim gradually fades to grey, our overdyed denim evolves with a fascinating indigo-tinged hue and greater depth due to the layered gradient of colours.
The Iron Heart Overdyeing Process
While “overdyeing” refers to the addition of a secondary dye to fabric, the technique we use to apply the dye is called “garment dyeing”. Put simply, this means we don’t just overdye rolls of fabric — we take a fully (well, almost fully) constructed garment and submerge it in a dye vat. In other words, it’s not just the fabric that’s overdyed — the stitching, tags, and sometimes, the hardware are also affected. Because various parts of the garment absorb dye differently (depending on thickness and construction), this process creates a distinctive, less even appearance that adds unique character. The only part of our jeans and jackets that’s sewn on after overdyeing is the leather patch, as the high temperatures involved in the process would destroy it.
Do We Only Overdye Denim?
Most of our overdyed garments are indeed made from denim, but the technique can be applied to many different fabrics. Over the years, we’ve offered overdyed variations of chambray, canvas, and even our signature ultra-heavy flannel shirts. We also don’t restrict ourselves to black dyes. Some models have used red and blue dyes to create vibrant tones, while lighter washes of white dye have been applied to soften the boldness of brighter colours — a technique most notably used for our highly sought-after 20th-anniversary flannel shirt.
Types of Dyes
Historically, Iron Heart has used sulphur-based dyes in our overdyeing processes. However, as we continue to shift toward more eco-conscious production, we now favour less hazardous direct dyes in most cases. One trade-off is that the older sulphur dyes (still used on our 14oz denim at the time of writing) not only coloured the fabric but also oxidised the metal rivets and buttons — giving them a pre-aged, vintage patina. Whether or not you appreciate this characteristic is, of course, a matter of personal preference. With our newer, direct dye methods, this tarnishing no longer occurs; however, we’re more than happy to make that trade-off in favour of more environmentally responsible practices. Below you can see the different results of the different types of dyeing.
Are There Any Other By-products of Overdyeing?
Yes! Overdyed fabrics often feel softer to the touch, and because the process involves very high temperatures with a lot of agitation, all potential shrinkage is removed from the garment. This means that you shouldn’t need to worry about further shrinkage, even when the garment is washed more aggressively.
That said, we recommend paying special attention to sizing. Overdyed garments often fit slightly smaller and tighter than their non-overdyed counterparts. In some cases, like with our overdyed flannel shirts, you may need to size up from your usual Iron Heart fit. As always, if you have any concerns or need sizing advice, don’t hesitate to get in touch.