Mid-century clothing labels often functioned as miniature advertisements. Manufacturers used technical textile terminology to communicate quality, durability, and modernity to consumers. Terms such as "Vat Dyed," "Mercerized," and "Sanforized" were not just manufacturing notes but selling points intended to distinguish garments in an increasingly industrialized market. Understanding these terms can help identify both the intended qualities of a garment and the technological developments that shaped its production.
Sanforization
Image via vintagehaberdashers.com.
Sanforization is a mechanical process used to pre-shrink cotton fabrics to reduce the amount they shrink after washing. Before sanforization became widespread, it was normal for cotton garments to shrink dramatically after their first few washes. A pair of jeans could lose several inches in size. Sanforization was developed to solve this problem by shrinking the fabric before it was cut and sewn into garments.
Sanforization Process
A simplified version of the process goes as follows:
- The woven fabric is dampened
- The fabric is fed onto a rubber belt or blanket.
- The rubber belt is compressed.
- As the belt returns to its normal length, it forces the fabric to compress lengthwise.
- The compressed fabric is dried and stabilized.
Sanforization History
The process was invented by Sanford Lockwood Cluett, an executive of the Cluett, Peadbody & Co. Cluett patented the process in 1928 and the name "Sanforized" comes directly from his first name, Sanford.
During the 1930s and 1940s, sanforization spread rapidly throughout the American textile industry because it solved the single largest frustration consumers had with cotton clothing—shrinking. By 1950s after WWII, many manufacturers prominently advertised Sanforized garments, often printing the trademark directly on labels, hangtags, or pocket liners.
Dating Sanforized Clothing
Starting in the 1930s, manufacturers proudly advertised Sanforization because it was new and highly marketable. By the 1960s, the process became increasingly standard in the industry. By the 1970s and 1980s, many manufacturers advertised garments simply as "Pre-Shrunk" rather than using the Sanforized trademark. While Sanforization was one of the most common methods of pre-shrinking fabric, not every pre-shrunk garment was necessarily Sanforized.
Vat Dyeing
Image via vintagehaberdashers.com.
Vat dye is is a dye that is insoluble in water until chemically reduced. Vat Dyeing is a process in which fabric is dipped into the dye vat, then exposed to air so the color oxidizes and bonds deeply into the fibers. The benefits of vat dyed fabric is that it had better resistance to fading, washing, sunlight, and perspiration. It was often advertised on workwear, military garments, denim, and childrenswear.
Natural indigo is actually one of the earliest vat dyes: it changes from yellow, in the dyebath, to green and then blue as the air hits it. Before synthetic dyes became widespread, indigo dyeing was labor intensive and inconsistent. Industrial vat dyes allowed manufacturers to produce garments with much greater color consistency and wash resistance.
Vat Dyeing Process
Vat dyes have to go through a chemical process before they can properly bond to fabric. First, special chemicals are added to the dye bath to temporarily make the dye water-soluble. This transformed version of the dye is called its “leuco” form. The fabric is then dipped into the oxygen-free dye bath so the dye can deeply penetrate the fibers.
Once the fabric is removed and exposed to air, oxygen causes the dye to change back into its normal insoluble state. This reaction locks the color into the fabric and creates the rich, durable finish that vat dyes are known for. Manufacturers would often repeat this dipping and oxidation process multiple times to achieve deeper, longer-lasting color.
Why Vat-dyed Garments Age Differently
Image of fabric being vat dyed via sharonburnston.com
Vat dyes, such as indigo are applied in a reduced, soluble “leuco” state, then oxidized back into an insoluble pigment inside or very close to the fiber. That gives them excellent wash fastness, which is the measure of a textile’s ability to retain its color and resist bleeding or fading during laundering.
Even though vat dyes penetrate fibers better than many dyes, a lot of the color still sits closer to the surface of yarns. As the garment is worn and abraded, the outermost dyed fibers gradually wear away first, revealing lighter inner fibers. This is responsible for giving vat-dyed garments a higher contrast fade instead of a flat wash-out.
Dating Vat Dyed Clothing
The term "Vat Dyed" appeared on American workwear labels from the 1930s-1960s. During this period, colorfastness was a major selling point. While the presence of a vat-dyed label cannot precisely date a garment, it is most commonly encountered on mid-century workwear, military uniforms, denim, and children's clothing.
Mercerization
Mercerization is a chemical process used primarily on cotton that makes the fibers stronger, more lustrous, and receptive to dyes. The result is a cotton fabric or yarn that often has a silky sheen, richer color, improved stability, and a smoother hand. Seeing this term on a vintage label means that the cotton was treated with a strong alkali solution to permanently alter the structure of the fiber.
Raw cotton fibers naturally exhibit a twisted, ribbon-like shape. During mercerization, the cotton is immersed in a concentrated sodium hydroxide solution. This causes the cellulose fibers to swell dramatically.
Mercerization Process
(a) Schematic illustration of mercerized process of cotton fabric; (b) The reaction mechanism of cotton fiber treated with NaOH.
A simplified version of the process:
- Cotton is wetted and cleaned.
- The material is immersed in a sodium hydroxide solution.
- The fibers swell and change shape. The flattened twisted cotton fibers become more cylindrical and uniform
- The material is held under tension. This prevents shrinkage and creates the characteristic luster.
- The alkali is washed out and neutralized with water or a mild acid bath.
The shine visible on mercerized cotton isn't a chemical coating on the fabric but a consequence of structural change within the fabric.
Untreated cotton fibers are irregular and flattened, which scatters light in many directions. After mercerization, the fibers become more circular and smoother, allowing them to reflect light uniformly. This is why mercerized cotton can resemble silk from a distance.
Mercerization History
Mercerization was discovered in 1844 by John Mercer. While experimenting with cotton and caustic soda, he noticed that fibers shrank, became stronger, and accepted dyes more readily. He patented the process in 1850. Mercer considered the improved dye affinity the most important benefit of the process because he had let the fibers shrink freely during treatment, as opposed to keeping them under tension.
The breakthrough came in 1889-1890, when Horace Arthur Lowe discovered that keeping the cotton under tension during the treatment developed a silk-like sheen. This transformed the process into a premium textile finish.
By the 20th century, mercerized cotton was marketed as a luxury material for its ability to imitate silk.
Dating Mercerized Cotton
By the Mercerization is generally a poor dating tool because the process existed since the mid-nineteenth century and became widespread during the early twentieth century.
Although no single textile term can precisely date a garment, understanding these labels can provide valuable clues about how a piece was made, marketed, and intended to perform. Whether indicating resistance to shrinkage, superior dye fastness, or a more luxurious finish, these processes reflected the textile industry's continual effort to improve everyday clothing. For today's collectors, they remain small but meaningful details that help tell the story of a garment's history.