Dry & Dry [15 Packs] Premium Cobalt Free Humidity Indicator Cards(Reusable 6 Spots)

Pure Junk:In a nut shell I'm not sure why these are even being sold.First I should mention that my amazon order of this product was never delivered to me. So I'm reviewing this exact item obtained through a different source with the understanding that this product is the same wherever it comes from. Branded "Dry & Dry".going purple and back:The biggest problem with this product is that it seems to render itself chemically inert in short order. I saw another review where someone put them in vacuum sealed containers and said that they came out unable to indicate at all. He seemed to think it was the vacuum that deactivated them but I have observed this behavior in less then a week with cards that have just simply been sitting on my desk. At first I thought that they were just highly iratic in their readings because I would have one card indicating 10% and another card indicating >60% sitting right next to each other. Over a couple days I came to realize that the most recent cards to be removed from the silica-gel-protected zip-lock bag that they were shipped in were indicating a higher percentage then the cards that had been removed first. I have now tested 6 of the 15 cards and they all have done the exact same thing. when taken out of the bag and exposed to about 50% RH they turn completely purple within 10 minutes indicating >60%. it takes them several hours and the begin to fall. At some point they seem to linger near an actual reading and then they begin to fall about 10-20% indicating each day or so until eventually they are completely green indicating <10% even though the RH is neer 50%. So if you pull a new card out each day and add it to the others you'll get results something like the photos I will attach.readability:Even if they were reliable, they are indeed very difficult to read. The spread on the cobalt style cards typically transitions in 1-3 dots so you can perceived the center line without much trouble but with these cards, I've seen the indication spread 5 of the 6 dots, making the actual reading really difficult.Pics:I will attach 2 images. They are the same photo the first one is exactly as the camera took it, but because they are so difficult to read I applied a simple color filter to the image to product the 2nd photo so that you can see what they are indicating a little easier. All of the cards in the photo had been sitting in 53% humidity for over 2 hours side by side. You be the judge!Caveat:I want to take just a moment to say that this company makes terrific silica gel. And they are great to deal with as well. I contacted them directly with this problem and they were painless to deal with. The shipped me replacement cobalt cards and even threw in a few extras. So I do recommend purchasing their products, just skip the cobalt-free cards and save yourself the wasted time. Or be warned if you don't test them and put them to use you might be seeing a falsely-green sense of security. :)Hope this helps some lost soul out there.

The color differentiation between the green indication and violet indication is so slight that it is virtually impossible to read. What is supposed to be violet is actually just a slightly darker green, but even the green is different across all of the dots, so there is no possible way to tell the difference. Either I got a bad batch, or these are completely useless. To make things worse, there isn't any way to contact the manufacturer/seller (same).

It's too hard to read, perhaps why none of the pictures shows anything other than 0% or >60%. The card says to use the grey value in between the green and the violet indicators but what I see is violet, slightly violet, grey, grey, slightly green, green. If I were to pick the most neutral grey it would be the 30% mark but it's been sitting for 24hrs in an area with 50% humidity. You can see in the attached picture, which I took on top of a catalog to prove it's not just a washed out picture.Update: I set out 3 fresh cards for almost a week at 45-55% humidity and as you can see it's looks like they're all only reading 30-40%. So I'd say this product would only be useful if needing to test to tell if a desiccant is working but you can buy those with built in indicators now.One other strange thing, if you put these in a vacuum sealed container they stop working, even after you remove them. I tried this with 3 different cards, all worked before but after putting them in a jar and sucking most of the air out they never worked again, all dots are green.

tldr;Out of the bag they do not work, all indicators remain green no matter what the humidity is.I am using for 3d printer filament along with the indicator silica beads from the same company. All the indicator spots have remained green while the the silica gel beads have already changed color to indicate saturation and increasing humidity. I left a couple on the table in the room to double check they work and they haven't changed either. Since this process took too long, it is no longer possible to return these.

I have calibrated gauges, so put these alongside to see what they did. Nothing worthwhile.