Hi, Cindy,
It is a myth. To determine a replacement schedule, we need to know the specified shelf-life of a product under a defined storage condition. I reached out to several suppliers in the US, UK and DE about 2-3 years ago, and no one is willing to tell me.
The reason is obvious: this is a low volume product. A catalog company like Talas or University Products (by the way, I found that they are using the same supplier) may have to buy in bulk and keep a batch for a long time, several years on their shelf. Same for the manufacturer. They make a production lot of reasonable size, which could last several years in their inventory. Without knowing when a production batch is made and without the expiration date on the product package, users cannot determine a replacement cycle.
Alternatively, I asked them to tell me the manufacturing data of a specific production lot currently on the market. They do not want to tell, for the same obvious reason. The Bluewool card product from Talas and University product has a # printed on the back of every card, which appears like manufacturing date + lot #. I tried to verify with them, but they didn't want to confirm.
As such, I think the best practice is: once we receive a shipment, we seal the bulk of it and store it in a freezer, only keeping a few for lab use, sufficient to last a few months.
By the way, I also compared Bluewool cards from different suppliers using Xe-MFT, and noticed that not only are the average fading rates different on BW-1 or BW-2, but also the gaps between BW-1 vs. BW-2, BW-2 vs. BW-3 are different. Not sure if these are related to manufacturer variation or due to aging period difference by the scale of years. Most likely both.
Henry
Original Message:
Sent: 6/9/2025 6:24:00 PM
From: Cindy Connelly Ryan
Subject: Blue Wools - replacement cycle?
Hi all -
I would like to get a sense for how frequently other MFT users toss their old blue wool standards and order a fresh set. Biannually? More often? Less often? When you run out? Or when you start to notice a drop in sensitivity for BW 1 and/or 2?
Our metric, admittedly, is a fairly loose one - when we notice a shift in performance, or just start to feel squeamish about them being too old. I feel this could be improved upon! (FWIW, we use loose cloth BW's, not the pre-glued cards).
best,
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Cindy Connelly Ryan
Library of Congress
Washington, D.C.
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