I have seen too many people buy the wrong high temperature glove for their needs. So, I want to explain how a high temperature glove works (or doesn't work), and how you can select the right glove(s) for you.
First, what exactly is a high temperature glove supposed to do?
The purpose of a high temperature glove is to delay the transfer of heat, from a hot object or region, to your hands, hopefully long enough for you to accomplish what you need to do.
Let's look at this word-by-word:
The purpose of a high temperature glove is to delay the transfer of heat ... Notice I said delay, not prevent. All the glove can do is slow down that heat transfer.
... the transfer of heat ... How is heat transferred? There are several ways: Convection, Conduction, and Radiation. For our needs, we're going to focus on the first two. Convection is when you stick you hand into a hot oven or kiln, and Conduction is when you actually touch the inside of your hot oven or kiln. The difference is important when it comes to
delay the transfer of heat ...
With convection, the best way to delay that heat transfer is to not let the heat get near you in the first place. For this, you want to
reflect the heat away. We do this by using a glove with an aluminized back. That aluminized material does a very good job of reflecting the heat! Unfortunately, they are also very good at transferring conducted heat! So, if you are going to actually be touching something hot (intentionally, or otherwise), they are not a good choice. Likewise, you never want to use an aluminized back glove if you're going to be touching hot glass, as the glass will stick to the glove!
Conduction, on the other hand (no pun intended), requires the use of an insulating material to delay that heat transfer. There are all sorts of good insulating materials out there (firebrick, space shuttle tiles, etc.), but since this is a glove, after all, we need a material that can move and flex. The most common insulating material used in high temperature gloves is wool. Wool is an excellent insulator: just look at all your warm wool clothes. And, the more wool you have in your glove, the better the insulation, and the longer it will take for the heat to get through. So, if wool is such a great insulator, why can't we just use wool gloves? The problem is, at the temperature we glass artists work, our wool gloves would catch fire! So, we need to come up with a way to protect the wool (so the wool can protect our hands).
This is where the high temperature materials come into play. We need a material that has a high burning temperature, is strong, and is flexible. In the old days, we used to use asbestos. Asbestos has excellent high temperature, strength, and flexibility properties. Unfortunately, there are some health concerns about using it, and it's use has since been banned.
As a replacement for asbestos, we have come up with a man-made material called Kevlar. Kevlar is a very strong fiber, and is used in many applications: bulletproof vests, aircraft structures, cut resistant gloves, and the like. It also has a relatively high burning temperature, and is quite cost effective, thus making it a good choice for our high temperature gloves.
We now have a two-layer glove: the face material is Kevlar, and the inner material is wool. The wool's job is to insulate (delay the heat transfer to) our hands, and the Kevlar's job is to protect the wool. Sounds good, right? But, working with hot glass, we can exceed the burning point of Kevlar (it can go up to about 1000° F. for brief periods). Now what?
That's when we start looking at some of the higher temperature (and more expensive) materials. One such material is polybenzimidazole (or PBI, for short). PBI was developed for NASA's Apollo project, and can withstand temperatures of over 2600° F. By blending PBI with Kevlar, we can make fabrics that have the high temperature rating we need.
Here, one very important point needs to be made:
The temperature rating of the glove is that temperature, below which, the face material won't burn! It has nothing to do with how hot your hands will get!
This is important, people! This is why so many people buy the wrong glove, for the wrong reason. I can put a 1000° glove on one hand, and a 2600° glove on the other, and grab hold of something hot with both hands, and both hands will get just as hot, just as fast! Remember, the insulator in both gloves is wool, and since both gloves will probably have the same amount of wool, both gloves will have the same insulating qualities, regardless of the face material.
Ok, we start off with with a wool glove (to keep our hands from burning up). Then, we add a layer of Kevlar (to keep the wool from burning up). Finally, we blend in as much PBI as we can afford (to keep the Kevlar from burning up). We're all set, right?
Maybe, maybe not. You see, gloves also wear out as much due to abrasion as they do to actually burning. It has been my experience that the more PBI one adds to a glove, the lower it's abrasion resistance. So, what do we do? We carefully select the right glove for the application. Here are my rules for selecting the right glove:
Rule #1: Gloves are a consumable. Buy the least expensive glove that does what you need it to do, and expect to have to replace it. Gloves are going to wear out. Gloves are going to burn up. Spending more money on a higher temperature glove doesn't necessarily mean that you're going to get any more useful life out of them. I figure that if you get 3-6 months out of a pair of gloves in an active studio, and 1 year in a casual studio, you're doing well.
Rule #2: Always have at least two pair of hot gloves in the studio: One for touching hot glass (and NOTHING else!), and another for all the 'grunt work'. Use your 'grunt gloves' for things like opening kiln and furnace doors, moving kiln furniture, moving heat shields, charging the furnace, etc. Save one pair of gloves for just touching hot glass. This way, you won't ruin your 'glass gloves' with grunt work, and you won't ruin your glass by using gloves that have been contaminated with foreign materials.
Rule #3: Use cover mitts, when possible. Cover mitts are wonderful is so many ways:
Rule #4: Carefully think about what you're going to be doing with your gloves, think about the heat transfer, and select the right material for the application. For example, when you are moving heat shields, opening furnace doors, charging the furnace, or using a ladle or a rake, ask yourself: How hot is the item I'm actually touching? Sure, it's hot enough that you need to wear gloves, but, is it 200°? 500°? 1000°? How abrasive is this process or operation to the glove? Where is the heat coming from?
In the above examples, all of the items you are actually touching are probably going to be under, say, 500°, are quite abrasive, and you will be exposed to as much convection heat as to conduction heat. In these cases, I would recommend an aluminized glove with a leather palm. Leather can easily withstand the temperature ranges needed, is much more abrasion resistant, and the aluminized back will protect you from the convection heat. Sure, the leather will eventually dry out and/or burn up, but remember Rule #1.
If you keep these rules in mind, and think about what you doing with your gloves, I am sure you can select the proper glove(s) for your situation. Sure, you may find that you need 2 (or 3, or 4) pairs of different gloves. But, you'll have the right tool for the job, and since you'll be using the right glove, your gloves will last longer. For further assistance, please visit our website to see our selection of high temperature gloves.