Iconic Williamsburg: Reb Yosef Rosenberger and His Shatnez Laboratory

By Y. S. Gold

Very little has changed at 203 Lee Avenue in Williamsburg in the eighty years or so since Reb Yosef Rosenberger, the hero of this forgotten mitzvah, founded the Shatnez Laboratory there. 

Upon arrival in New York, he soon discovered that in America, the mitzvah of Shatnez was all but forgotten. He would make it his life’s mission to educate the public about this mitzvah, and to found the first laboratory for checking for shatnez in America.

It was a strange new reality in America. Back home, when someone wanted a suit tailored, he would purchase fabric and bring to the tailor who would fashion a suit. Thus, shatnez was not such a concern, because no G-d-fearing Yid would purchase wool and linen for a suit. Here, in America, companies would sell suits off the rack, and many, if not most, contained shatnez.  

Reb Yosef would serve as the shliach from Shomayim to save American Jewry from transgressing this forgotten issur. 

He was alerted to this reality when a friend, knowing that his father had tailored suits back home, asked him to check whether his wool suit contained linen. Reb Yosef took the suit around to a number of tailors—none of whom could confirm whether or not the suit contained shatnez. It pained him greatly that the mitzvah was forgotten, and he resolved to do something about it. 

He began traveling to the Garment District in Manhattan every day to educate himself and learn about the various fabrics that are sewn into clothing. He worked as a machine operator in a number of shops, all so he could learn the trade, the methodologies, and technologies that were utilized by clothing manufacturers.  

A Lifelong Mission 

After some time gaining experience in the garment shops, he figured out the methods of ascertaining whether a garment has shatnez. He was ready to open his own laboratory for checking clothing. In 1941, he opened the first laboratory inside the Agudah building at 616 Bedford Avenue. 

Since the founding of the lab in 1941, Reb Yosef was always there, rarely taking a vacation. He worked day and night to serve the thousands of Yidden who came to him with their clothing. He estimated that in the first twenty years of the existence of the lab, he checked around 150,000 articles of clothing! 

But Reb Yosef did not stop there. He knew that his laboratory was only one phase of his work. If he wanted to change the landscape, he would need to educate the public, and so, late at night, after hours and hours of work at his sewing machine, he moved over to his typewriter, cranking out literature warning the public about the proliferation, and the severity, of shatnez. 

He would place advertisements in the papers warning the public about this issur, and he printed brochures with stories and halachos about shatnez. He paid for all of this from his own funds. In the days before computers, Reb Yosef came up with brilliant, eye-catching drawings for his advertisements. 

Many of our readers will remember the luach that hung in many shuls with the warning, treifos nit, shatnez yoh? This was part of Reb Yosef’s efforts—spending the little money that he made from the laboratory to further educate the public about this important mitzvah. Many will also remember that, even into his old age, he would make his way around the Shuls all over to make “appeals” for shatnez. 

In addition to his dedication to shatnez, Reb Yosef was involved in myriads of chessed activities. 

Reb Yosef was niftar on the 7th of Cheshvan of 1997 following a lifetime of dedication to this mitzvah of shatnez in Williamsburg of yore.