I’ve debated about posting this for some time now, but recent events have prompted this post.
For over a year now, Revere Glass Studio has owed my company, Aura Visual Concepts/Aura Lens Products, over $400.00 for some eyewear that I sold to him on open account, net 30 days. About 2 months ago, I received payment in the amount of $50, with the promise of an additional $50 each week until the account was paid in full. Of course, the balance never arrived.

There are reports of other shady deals with Revere as well, as can be seen here: http://www.thegldg.com/forum/showthread.php?t=28904 such as cancelling classes without notice, not returning borrowed equipment etc.

Even though Revere brings in some high talent artists, his business practices leave much to be desired.

Accordingly, I recommend that you skip taking classes at Revere Glass Studio and you give your business to other reputable studios.

I purchased a pair of your glasses 4 or more years ago. Lately, I’ve noticed that my eyes are hurting when I am done at the end of the day. Does the filter material “wear out” over time?

Answer: No. The filter elements are part of the glass matrix and cannot/do not fade. Welding filter glass uses iron as the major filtering element. AUR-92/ACE glass uses didymium/neodymium/praesodymium plus other “rare earth” elements. These elements are mixed in with the silica when the glass is being melted by the manufacturer.

The manufacturer of the glass routinely tests its glass over time, keeping samples of each melt and subjecting them to various tests to determine transmission over time and exposure. Schott Glass Technologies, for example, has samples of didymium that go back over 50 years, and that glass still has the same transmission characteristics that it had when it was first made.

What is more likely is that over time, your skills have improved from the time you first bought your glasses. You may be working longer hours, you may be using different techniques, and you are certainly working with different formulations of borosilicate glass (especially the colors). You may also be doing more fuming now than you did when you first got your glasses.

The bottom line is that you have perhaps “out grown” your current filters and most likely need something with more filtration.

The title of this piece isn’t meant to be snide or churlish, just what I’m feeling right now.

Did your grade school have a naughty bench? You know, the bench or chairs outside of the Principal’s Office? Where the ‘bad kids’ sat before getting lectured for their behavior?

Yeah, that place.

I admit it. I’m an ass. I’ve taken the first step: admitting to a problem. The next steps are even harder, but today I’m trying my best.

If you keep count of such things, you may notice that the blog here is a bit smaller. I’ve deleted some of my postings from last year, especially those that called out certain people and places, for perceived (at least MY perception) wrongs.  I didn’t deleted those posts to make myself look better, they were deleted to start a healing process. Certain of those posts strayed from the mission of this blog, which was to create a place that was dedicated to glassworking studio safety. Some of the deleted and edited posts took things too far and instead it became a pulpit to bluster and be a blow-hard.

I’ve wronged a fair number of people over the years, both in word and in deed. I know that a goodly number of those will never ever forgive me. That’s fair enough. But I hope that at some point in time I can at least look them in the eye and not see disgust and anger.

One person in particular deserves mention here: Pam Dugger.  Pam and I used to be very good friends. Until, that is, I first put her into an untenable position and then sat on the sidelines like the Peanut Gallery and criticized her for (my perception of) inactivity. I wanted her to do what *I* wanted her to do, which wasn’t fair to her or to our friendship or the membership of the ISGB at large. I used our friendship to attempt to get the things done that I felt needed to be done. I destroyed something that should have been cherished and nutured. I don’t know that I will ever be able to sit down across a table from her again and laugh at the general silliness of the world we live in. And I am a lesser person for that. Pam, I am sorry. I hope that at some time in the future you can find it in your heart to forgive me.

Barb Svetlick: I betrayed your trust in me. I thought I was doing the right thing, but by all reckonings, it was probably the worst thing I’ve done in quite awhile. I am sorry. I hope that you too can find it in your heart someday to forgive me.

Robin Aragorn: I wrote something extremely stupid to you in the heat of an argument and it has burned in you for at least a year and a half. We’ve battled and exchanged heated words across several forums over the past 18 or so months and they all finally came to a head this week. I wish I had been in the office on Wednesday so that I could have apologized to you then and there, but I wasn’t and here we are.

I am sorry, Robin. Sorry for the stupid words, the arguments and the name calling. I’d love to be able to turn back the clock and take back everything that was said and done, but I can’t. I am glad that you continued to stand up for yourself and speak out against what I’d written. Thank you for that. I don’t know what more I can do, but you have my full and complete apology.

There are others that I’m sure I’ve offended and hurt over the years. If you read this, send me an e-mail m.aurelius@auralens.com. I’d like to apologize, either privately or publically.

I’m going to set this post so it stays on top for awhile so folks get a chance to see it.

Per eye, approximately $7,200.

My mother, still “young” (in her early 70’s), just had cataract surgery in both eyes over a two month period of time.

$14,400 for both eyes. Plus not having perfect vision for up to 2-3 weeks afterwards, having to avoid bright lights for 6-8 weeks. If my mother had been a torch worker, she would have been out of work for close to 4 months.

NIOSH and OSHA have determined that the IR TLV (threshold limit value) to the unprotected eye is 10 mW/CM2 for time periods greater than 16 minutes. (10 mW is .010 Watts)

There are two critical areas to take into account when trying to determine the exposure value of IR radiation. The first critical area is the heat source, be it a furnace, glory hole, or torch. These heat sources typically run at a higher temperature than the glass being worked, and thus are a higher hazard. The second critical area is the piece being worked. The piece will typically have two zones, the heated area, or that portion of the piece that is currently being worked, and the rest of the piece, which is radiating at a lower temperature than the worked area. All three of these areas contribute to the total radiation that the glassworker is being exposed to.

The basic forumula is: Total Exposure = A1 + A2 + A3, where Ax are the areas referred to above.

The basic formula for calculating exposure is: R * (A / (2 * 3.14159 * r²) ) Where R = Radiance of the object in watts per square centimeter, A = the area of the radiation, in square centimeters, and r = the distance to the eye from the heat source, in centimeters.

The following is an example calculation, based on a medium sized torch working a large borosilicate piece.

The flame calculation is this: For a 3500 degree flame (average), Radiance is 4 Watts per square centimeter This may sound very low, but keep in mind that the blackbody calculations are based on the mass of item. A flame has very little mass for the amount of heat that it generates, which skews the Radiance calculations.

If the flame is one inch wide at the base and (for example) averages 8″ long, the area of the flame is 8 square inches, or 51.61 square centimeters. The distance of 16″ equals about 40 centimeters.

Plugging into the formula above, E = 4 * ( 51.61 / ( 2 * 3.14159 * 402) )

Which reduces to: E = 4 * ( 51.61 / 10053 )

Which further reduces to: E = 4 * .0051

Which results in: E = .020

The flame alone contributes 0.020 Watts per square centimeter at the eye.

For the working area, let’s assume that the temperature of the glass is 1800 degrees (which is a radiance of 10 Watts per square centimeter), and the area being worked is 5 centimeters by 10 centimeters (or 50 square centimeters). We’ll keep the same working distance of 40 centimeters.

E = 10 * ( 50 / 10053)

Which reduces to: E = 10 * .0049

Which results in: E = .049

The working area contributes 0.049 Watts per square centimeter at the eye.

For the nonworking area, let’s assume that the temperature of the glass is 1100 degrees (which is a radiance of 2 Watts per square centimeter), and the nonworking area equal to the working area, or 50 square centimeters). Remember that if you are building a large piece, the nonworking section will continue to grow, so keep that in mind. We will also keep the same working distance of 40 centimeters.

E = 2 * (50 / 10053)

Which reduces to: E = 2 * .0049

Which results in: E = ..010

The nonworking area contributes 0.010 Watts per square centimeter to the eye.

Add these areas up, 0.020 + 0.049 + 0.010 and the result is 0.079 Watts per square centimeter to the unprotected eye.

Now, let’s figure the protection value of the various filters. Remember that the IR TLV is 0.010 Watts per square cm.

Phillips Boroscopes Shade 3 passes an average of 55%, so 55% of 0.079 = 0.043 (4.3x TLV)

Phillips Boroscopes Shade 5 passes an average of 40%, so 40% of 0.079 = 0.031 (3.1x TLV)

Aura Lens AGW 203 passes an average of 3.4%, so 3.4% of 0.079 = 0.002 (20% of TLV)

Aura Lens AGW 286 Shade 5 passes an average of 1.5%, so 1.5% of 0.079 = 0.0012 (12% of TLV)

The following is an example using a small torch similar to a Nortel Minor, and making a soft glass bead. The bead is two centimeters square, and in this case we will assume that because the bead is so small, that the entire bead is a consistent temperature.

If the flame is one half wide at the base and averages 6″ long, the area of the flame is 3 square inches, or 19.35 square centimeters. The distance of 16″ equals about 40 centimeters.

Plugging into the formula above, E = 4 * ( 19.35 / ( 2 * 3.14159 * 402) )

Which reduces to: E = 4 * ( 19.35 / 10053 )

Which further reduces to: E = 4 * .0019

Which results in: E = ..0076

The flame alone contributes 0.0076 Watts per square centimeter at the eye.

For the working area, let’s assume that the temperature of the glass is 1200 degrees (which is a radiance of 8 Watts per square centimeter), and the area being worked is 2 centimeters by 2 centimeters (or 4 square centimeters). We’ll keep the same working distance of 40 centimeters.

E = 8 * ( 4 / 10053)

Which reduces to: E = 8 * .0004

Which results in: E = .0032

The working area contributes 0.0032 Watts per square centimeter at the eye.

Add these areas up, 0.0076 + 0.0032 and the result is 0.0108 Watts per square centimeter to the unprotected eye.

Now, let’s figure the protection value of the various filters. Remember that the IR TLV is 0.010 Watts per square cm.

Didymium passes an average of 66.7%, so 66.7% of 0.0108 = 0.0072 (72% of TLV)

AUR-92/ACE passes an average of 59%, so 59% of 0.0108 = 0.0063 (63% of TLV)

The following is an example using a small torch similar to a Nortel Minor, and making a borosilicate bead. The bead is two centimeters square, and in this case we will assume that because the bead is so small, that the entire bead is a consistent temperature.

If the flame is one half wide at the base and averages 6″ long, the area of the flame is 3 square inches, or 19.35 square centimeters. The distance of 16″ equals about 40 centimeters.

Plugging into the formula above, E = 4 * ( 19.35 / ( 2 * 3.14159 * 402) )

Which reduces to: E = 4 * ( 19.35 / 10053 )

Which further reduces to: E = 4 * .0019

Which results in: E = ..0076

The flame alone contributes 0.0076 Watts per square centimeter at the eye.

For the working area, let’s assume that the temperature of the glass is 1800 degrees (which is a radiance of 10 Watts per square centimeter), and the area being worked is 2 centimeters by 2 centimeters (or 4 square centimeters). We’ll keep the same working distance of 40 centimeters.

E = 10 * ( 4 / 10053)

Which reduces to: E = 10 * .0004

Which results in: E = .0040

The working area contributes 0.0040 Watts per square centimeter at the eye.

Add these areas up, 0.0076 + 0.0040 and the result is 0.0117 Watts per square centimeter to the unprotected eye.

Now, let’s figure the protection value of the various filters. Remember that the IR TLV is 0.010 Watts per square cm.

Didymium passes an average of 66.7%, so 66.7% of 0.0117 = 0.0078 (78% of TLV)

AUR-92/ACE passes an average of 59%, so 59% of 0.0117 = 0.0069 (69% of TLV)

AGW-203 passes an average of 3.4%, so 3.4% of 0.0117 = 0.0004 (0.4% of TLV)

Commentary on the above calculation for small borosilicate work:

In light of the above calculations, it would be easy for a torch worker to assume that they don’t need special eyewear to work with boro. After all, for a small bead, the standard soft glass filters seem to be blocking enough IR radiation, so that’s ok, right?

Correct, but only so far as it goes.

There are two other issues that the torch worker needs to be aware of:

First is the assumption of relative flame size. In the given example, the flame is fairly small, in the Nortel Minor range. If you are using a larger torch or using a larger flame size than what is noted above, then the above calculations would need to be redone based on YOUR torch flame size.

The second assumption is that the only thing the torch worker needs to be careful of is IR. This is untrue. High Intensity Visual radiation, as referenced here: http://mikeaurelius.wordpress.com/2007/12/25/visible-light-hazards-and-the-glassworker/ discusses visible light “flares” across the visible spectrum that are in excess 10,000 lumens (1 lumen is a candle flame). 10,000 lumens is direct sunlight on a white sand beach.

HIV is present in working soft (especially the new silvered soft glass colors) and borosilicate glass, but is more pronounced in the boro colors. Boro colors contain higher levels of metal and mineral colorants, and as these metals and minerals burn off inside the flame, they emit visible light “flares” that can easily exceed 20,000 lumens. Additionally, anyone who fumes soft or borosilicate glass can be exposed to silver/gold “flares” that can exceed 30,000 lumens.

The recommendations that I made in that article still apply, no matter the size of the piece you are making:

Proper filter eyewear is an absolute requirement for anyone working with hot glass.

Clear lenses do not provide proper filtration of UV, HEV or HIV wavelengths and should not be worn during any hot glass operation.

Didymium and ACE (Amethyst Color Enhancement) filters by themselves provide safe filtration for soft glass workers but should never be used by borosilicate glass workers without additional visible light filters. If you have light colored eyes, you may wish to consider adding additional filtration depending on your personal sensitivity to bright light. Additional filtration may be required by anyone working with glass that contains silver additives or any other material that create bright visible light flares.

Individuals working colored borosilicate glass must always wear a shaded lens that provides a maximum of 10 to 12 percent visible light at the HEV wavelengths (which translates to a welding shade 3.0). Darker shades must be worn when working with glass that generates very bright visible light flares, such as quartz, or when working with metals such as silver or gold.

Ensure that your eyewear is providing proper filtration. Your supplier should be able to provide a transmission graph showing what your eyewear transmits at specific wavelengths.

Altitude and air temperature make a substantial difference in the performance of any ventilation system. The calcuations I have provided here: http://mikeaurelius.wordpress.com/2007/12/25/ventilation-basics-part-two/ are based on sea level and 70 degrees F.

In the calculations, the only variable that needs modifying is VP, Velocity Pressure. The standard calculation is (V/4005) squared.

When applying temperature and altitude corrections, use the following equation: VP = ((V/1096.7) squared) times ‘density of the air in pounds per cubic foot’.

The following table gives standard Density of air in pounds per cubic foot.

As an example, let’s go back to example one on the above referenced link and apply both an altitude and temperature correction to the design.

Example:

CFM = 1300

Altitude = 5,000 feet above sea level

Temperature = 100 degrees (summer average)

Duct size = 6″ round (or .196 square feet) Use the area of a circle formula (Pi times radius squared) divided by 144.

Total run = 6 feet.

Number of Bends: 0

Loss Factor: 0.11 (from Table 1)

Solve for Velocity: 1300 / .196 = 6632 Feet per Minute

Solve for VP: (6632/1096.7) squared times .059 (from table above) = 2.15

Solve for SP: 2.15 times 6 times .11 = 1.42 inches of pressure

 As you can see from the original calculation in example 1 where the calculated static pressure was 1.80 inches, increasing altitude and/or temperature decreases the static pressure in the system. This is due to the fact that at higher altitudes, air is less dense than at sea level.

However, note the temperatures. If your average temperature is below 70 F, your static pressure is going to increase, because cold air is more dense than warm air. This means that your ventilation system is going to be slightly more inefficient in the winter than it will be in the summer.

From the ISGB forum:

Hi , right now I’ve been using the system Vince described in the Drew Fritts book. I had been using a minor and everything worked well.
Recently purchased an Lucio torch from Carlisle. I noticed I needed to upgrade my ventilation system. So I like to start from scratch, build a new hood etc. My room is 8 x 24.
I have also read an interesting article, and would like to get your thought on it please. Here is a link.
http://andreaguarino.com/ventilation/

I took a look at Andrea Guarino’s website and the link on her ventilation system. If you are a regular reader of my blog, you know my feelings on open duct ventilation (I don’t believe they work and don’t recommend them).

I found quite a few ventilation fallacies being perpetuated in the design description. Here’s a few:

Note: There is some turbulence caused by the ribs of the flex tubing however an adequate fan like the one recommended can overcome the small losses caused by this. An artist needs to be able to use flex tubing when curving around obstacles. Also, it is important to have a system that can be cheaply and quickly assembled rather than worry about small turbulence losses due to the ribs of the tubing.

“Some turbulence” is right. When calculating static pressure, part of the calculation is loss due to friction and turbulence from the relative roughness of the material being used in the ducting. The “standard” material used in ducting is galvanized metal, which has an average roughness of 0.0005 inches per foot. Corrugated ducting, such as shown in the website referenced above, has an average surface roughness of approximately 0.25 inches per foot, or 500 TIMES more roughness. This translates directly to 500 times more turbulence, which results in a huge increase in static pressure.

As an example, the fan shown is 289 CFM. Let’s assume a 6 foot duct run. If normal galvanized ducting is used, the static pressure including friction loss from the duct is 0.06 inches. For corrigated ducting, the static pressure including friction loss from the duct is 2.60 inches. Many fans cannot handle such high static pressures.

Now, scroll down a bit and look at the picture of the Mini-CC flame. showing the flame (poorly adjusted flame, mind you), being sucked down into the duct. I’d like to know how any glassworker can work in a flame where all the heat is being sucked away from the torch so fast. This is another reason why I don’t like duct-type ventilation systems. You need far more air movement per duct area in order to trap all the fumes than you would need for a conventional overhead hood. When the flame starts to be affected by the air movement, there is a serious design flaw that needs to be remidied. Even the next picture down, with the rod warmer attachement over the duct face shows similar flame distortion from air movement. The author notes that the flame distortion shows “the power of the system”, I’d counter that with “the flame distortion shows that you are moving too much air and your glass work will chill faster than it needs to.” This isn’t about P-O-W-E-R, it is about exhausting bad air, but only the bad air. A properly designed overhead hood or workstation enclosure is not going to distort the torch flame at all.

From LE:

My studio is a separate building and my propane tank and regulator are in a ventilated box my husband built sitting on a ledge attached to the outside of the building. He ran the standard hose that came with the torch (or I my have purchased it separately) through a small hole about a foot from the floor which is about 4 feet to my torch. The small hole has a pvc pipe inserted with the hose running through it and then a wood plate on the ouside and inside holding it in place. The hose also has insulation stuffed around it. Okay, now it all looks fine to us – but the experts out there, are we missing some important safety concern? Thanks in advance!

On the surface, this sounds like a marvelous idea. Make a hole in the wall, line it with PVC, insulate it, and run the rubber hose through it.

Unfortunately, it is an illegal installation. The National Fire Code (NFPA) states that all wall penetrations must be accomplished with hard wall metallic piping. The piping can be copper, black (iron) pipe or stainless steel. There must also be a shut off valve on either side of the wall. On the inside of the wall, the pipe must extend to within 5 feet of the point of use, and if the point of use is further than 10 feet from the inside shut off valve, the line must have an additional shut off valve at that point (torch valves do not qualify).

more the engrish

I’ve been sleeping all night long. That’s an amazing statement, actually (despite the current US economic worries). You see, I have sleep disturbances. Not apnea (although the sleep test I took did indicate occasional apnea, 8 episodes in 7 hours of sleep), buy hypopnea, or shallow breathing during sleep. At one point my oxygen saturation fell to 82% (normal is considered mostly anything above about 96%). I occasionally snore as well.

I now have a CPAP machine next to my bed, set at 11 centimeters (air pressure). The first couple of nights were very interesting, I’d wake every couple of hours (as usual) and adjust the mask, or scratch my nose, and have to put the machine back on the low pressure ramp up (ramps from 4 cm to 11 cm over 30 minutes), roll over and go back to sleep. Wednesday night was the first night that I can remember in a very long time that I essentially slept all night long. I think I woke up once around 2 AM to readjust the mask, then went right back to sleep.

I’ve had my machine for just under one week, and I have to tell you that I feel so much better: well rested and mentally alert. I can’t wait to see what happens over the next month!

If you have problems sleeping at night, I strongly recommend that you check in with your local Ear Nose and Throat Clinic and ask them for a sleep study to see if you have a problem with sleep disturbances. It just might change your life for the better!