UNIVERSITY of DELAWARE
DEPARTMENT of CHEMISTRY and BIOCHEMISTRY

 

Glass Shop Tips

(I will add new items occasionally)
 

 

OOPS!! Can my glassware be repaired??

The answer depends simply on where the break happens to be, the extent of the damage and cost of glassware. Is it worth it to repair something like a test tube or basic pipette? Not usually. However many items (sometimes very expensive) are thrown away because someone feels it is unrepairable when in fact it can be "saved". If in doubt bring the item to the Glass Shop for a quick evaluation. I will be able to tell you the likelihood of repairing it, whether it is worth repairing, and to give you an estimated completion date.

Remember...the Glass Shop is here to help you. Don't hide or throw away damaged glassware because eventually you or someone else will need it again. This can cause an emergency for everyone (including me!) that could have been easily avoided. In some cases, depending on damage assessment, I may ask how apparatus was broken. This is only so I can consider whether a different design or modification may be stronger for your particular application. "It really doesn't matter to me who broke it". Bring it down to the shop so we can help keep your groups' research flowing smoothly.

How can I remove the brown rust from my condenser?
Try filling the coil with a 25% - 35% solution of hydrochloric acid, and letting it sit a couple hours (safely in a hood of course). Label it so the hazard is well understood by all. Then rinse thoroughly and repeat process if necessary. You can plug either the inlet or outlet to prevent leakage. Never plug both ports. Be sure to wear appropriate safety gear, follow proper acid handling/ disposal procedures.
Proper Storage of Glassware

Abrading the strong smooth surface of glass greatly reduces its strength in various ways. It also allows moisture to weaken it further. It is very important that you use and store labware properly. Put items in separate clear plastic bags before putting in drawers. This will allow you to see item easily, but prevent scratches. Except for fitting joints together or other specific operation, glass touching glass (or glass touching metal) are to be prevented whenever possible. This is even more important when glass will be used for vacuum or pressure applications.

10 Important Do's and Don'ts for Vacuum Systems
1. Never assemble glassware to lateral bars on your racks. Instead, use vertical bars to hold the finger clamps supporting your manifold and traps. Lateral bars will allow glassware to slip downward.

2. When starting-up a new vacuum line or one that has been exposed to air, it is best not to overfill the dewar. New or exposed systems have considerable amounts of water that is adsorbed in the glass. Thus, it is best to fill your trap-dewars to about 1/3 capacity and wait another half-hour or so until you fill the dewar all the way to the top. This avoids pressure spikes that occur when the liquid N2 boils-off and the condensate is collected too high in the trap.

3. Never use cryogenic traps on a leaking vacuum system. Oxygen and other materials can be trapped as a solid. Which in turn can clog the vacuum throughput and present catastrophic conditions from pressure build up as the solid melts to gas and increases volumetric pressures by factors of x600 or greater.

4. Restrict the use of silicone greases to traps only and avoid using the substance on adapter joints, stopcocks and orings. Silicone grease has a very short life span1 and tends to polymerize through out a vacuum system. This makes cleaning a system very difficult when it comes to repairs. In addition silicon dust can cause sensitive electronic equipment to fail. Instead, use Apezion M grease for joints and orings and use Apezion N for glass stopcocks. Both have longer lasting properties, the latter is more expensive but provides a lubricant for rotating stopcock plugs.

5. If you frequently empty traps or remove joints, silicone grease is an economic alternative. However, users should remove old grease and apply a new coating as often as possible. This will help avoid having your glass joints becoming permanently seized together.

6. When cleaning glassware in a base-bath, never soak joints that are connected together. Base baths can chemically fuse the two inter-locking pieces into one permanent piece.

7. When shutting down a system, always vent your traps before you turn-off your mechanical pump. This will avoid the back-streaming of pump oil into your system and allow the volatiles in your trap to boil-off without dangerous pressure build-up.

8. Hi-vacuum glass stopcocks should always have indexed numbers that match the plug to the barrel. These parts should not be interchanged.

9. Tygon and rubber hose tend to weld onto glass. To avoid accidents consider hose adapters that allow you to attach a hose to removable glass components otherwise always use razor blades to cut away old hoses.

10. Glass breaks only when two combined effects take place: Force & Flaws. It is important to always consider ways to reduce these effects. Over time flaws are inevitable. So use extra care on older glassware.

* Dow Corning silicone grease has a product shelf-life (in the tube) of about 18 months. When exposed to light or vacuum the grease can degrade in about two-weeks.

What exactly is a Base Bath? I heard it can damage my glassware...

Base baths serve a great purpose when cleaning "dirty" glassware. However, due to the fact they can severly damage glass, do not leave soaking any longer than necessary. Make a note on how long it takes to clean each particular residue and then use a timer. It can take a few minutes to a few hours. NEVER soak over night because it will remove a layer of glass and weaken/ frost the surface. Always separate glass joints before soaking. A base bath can actually chemically bond them together permanently.

Recipe for Preparing a Base-Bath Cleaning Solution:

* Put on thick black gloves, rubber apron, eye protection, and a face shield!
* Get a large plastic container (~5 gallon)
* Add approximately 200-300g of solid KOH pellets (sometimes NaOH is substituted)
* Add 4 L of ethanol (sometimes methanol or isopropyl alcohol is substituted)
* Carefully add 1L of deionized water
* Leave the bucket in secondary contain (i.e. sink) until KOH is dissolved and it has cooled back to room temperature before storing
* Replace cover to plastic container.
* Label container with current date and a sign that says “DANGER: BASE-BATH SOLUTION”.

Always use an apron, eye protection, respirator (or hood) and thick black gloves when manipulating glassware around the base bath! Rinse gloves after use to prevent spreading caustic all over your work area.

HIGHLY CAUSTIC- Follow all UD OHS chemical safety regulations as well as the precautions above.

Pressurizing Glassware

NEVER pressurize any glassware unless it was made for that purpose. Never introduce any more pressure than glass is rated for or more pressure than you need. Use a pressure release valve in case of regulator failure. A glassware explosion can be deadly.

ALWAYS- ALWAYS- ALWAYS shield pressurized glassware properly. ASK for assistance from faculty adviser if you are not sure.

Stuck Stoppers, Joints and Stopcocks

1.While holding "close" to ground portion , try rocking while pulling and turning gently, Turn stuck joints 90 degrees and repeat. Try this 5 or 6 times.

2. Heat “quickly” with heat gun or "soft" flame (if no solvent or other flammables are present) and repeat above. If heated correctly the outer joint will expand away from the inner in about 10 seconds (or less) allowing removal. If heated too slowly or overheated the inner joint will expand also and you must let it cool completely before repeating. Joints or glassware that has been heated above 490c should be brought to the Glass Shop for lehr annealing as soon as possible to prevent breakage.

3. If all fails, bring glassware to the Glass Shop for a demonstration of these, or other removal techniques.

As always...wear eye protection and be sure the vessel is open to atmosphere to avoid pressure build up. Also be very aware of grease inside joint or other compounds you may be heating. Some can be quite hazardous and should only be heated safely inside a hood.

Usually frequent "greasing" will prevent this problem. If you cannot use grease in your particular application it is best to use a teflon sleeve to prevent sticking.

"External" Stress relief of vacuum system

When you clamp a vacuum manifold or attached vessels, be sure you tighten with even pressure from both arms of the clamp. This will prevent a torquing of the glassware and unexpected breakage from occurring.

 

Removing rubber tubing from apparatus.

When pulling hoses off of glass hose barbs attached to glassware, hold as close as possible. If it does not slide off easily you should slice tubing with a razor. This will help prevent hose barbs from being snapped off.

 

Tightening ultra tore fittings

When tightening an ”ultra tore” o-ring type fitting, be sure that glass tube is not bottoming out in the metal fitting. If it is left touching the metal seat it can chip or break during use. Insert tube fully and "loosely snug" the fitting. Then pull the tube 1/4" away from the bottom before the final tightening.

 

Toepler Pump, mercury diffusion pump or other glassware containing mercury
It is always wise to place your pump or mercury containing glassware inside of a plastic vessel in case of breakage. A cut off nalgene, bleach or other proper size readily available container works great.

 

Importance of vacuum stopcock maintenance

I realize that no one wants to stop to clean and re-grease glass hi-vac stopcocks. However as you all know, after you open and close valve repeatedly it becomes harder and harder to turn. This will eventually lead to a leak or breaking off the entire stopcock from your manifold. This will happen even faster if you warm with a heat gun. Make the time to keep your system running smoothly, or next time  try using a new style teflon hi-vac stopcock.

 

 

What type of glass is it??

Although a true test to determine glass type is difficult at times, I have a few suggestions for making a fast logical guess. Most glasses used in research are of 3 "basic" types:

Pyrex/ Borosilicate- If you look at the ends of the tube they will usually appear light to medium green.

Quartz/ Vycor- Ends will appear white.

Soda lime, Flint or other Soft glass- Ends will usually be dark green, or any shade of blue.

Be aware that if the glassware is graduated or has color decals, the ends will possibly show that color (especially blue) giving a false indication of glass type.

If you need it tested further or require a compatability test.... bring items to the Glass Shop.

 

 

Cutting Flat (Plate) Glass

 

Scoring/Scratch Method

Cutting flat plate glass may be easier if you follow these tips. Always wear protective eyeware and gloves!

Typical flat glass cutting tools: Wheel (or diamond type) cutters. Cut running pliers (if needed)


1. Be sure your scratch (score) mark goes to both edges of the plate (and make only one scratch). Multiple scratches can cause a bad cut.

2. Curved lines can be produced and cut as well. Make one good score by applying even pressure on the glass with the cutting tool.

3. Wet the scratch with water ( a spray bottle will work fine) just prior to breaking. If glass pliers are used, apply them at the edge where the scratch ends. If using the "tap" method, tap on the glass surface opposite side of the scratch. Start at the scratch end and follow or chase the break across the glass plate.

4. An alternate way of breaking the glass plate is to place a very small diameter rod under score mark(score should be facing up). Wet score. Holding each end, press down until it breaks cleanly.

If you are attempting to remove a strip of glass less than 25mm in width, it is recommended that glass pliers or the "tap" method be used.

Cutting tools come in different forms and wheel angles. Wheel angle guidelines are 130 -140° for window (float) glass and 88 - 114° for borosilicate glasses.

Feel free to come to the glass shop for a demonstration.

Snapping Glass Tubing


To cut glass tubing you need a "sharp", triangular file or a glass scoring knife. Place the tubing on a hard, firm surface, hold firmly with one hand and mark a scratch with the file where the tube is to be broken. You need to press with the file and you can hear it cut the surface, leaving a white mark. For small diameter tubing (under 10mm) you only need a small scratch.

Wet this scratch with a little saliva or water, turn the tube so the scratch is facing you. Grab tubing with thumbs on either side of scratch. Bend (elbows pushing away from you) while pulling the tubing lengthwise to open up the scratch. You should be pulling apart more than bending for best results. NOTE: If you just push elbows away from you and bend tubing it will chip or break badly. For a larger tubing (10mm-30mm od) you may need to make a slightly longer scratch first. Practice and you will find it easy to get a nice break in no time. I like to firecut or saw tubing above 30mm for best results.

The potential to get cut is greater snapping tubing as opposed to cutting plate glass. I suggest you come to the glass shop for a demonstration before trying for the first time.

For extra safety hold the tubing in a cloth or wear cut proof gloves.

 

Basic Glass Making Formulas


The following was provided for entertainment or educational reference only. Some of the ingredients may be harmful to you or the environment, especially when heated. The actual process (as well as safety information) should be researched fully before ever attempting to "make" glass. If you require further information please contact the glass shop.

There are literally hundreds of glass types and variations attainable. Below are just a few of them.


  Clear Plate Glass
Quartz Sand 100
Lime 12
Soda Ash 33
Iron Oxide 1.92
Potash (refined) 6
Manganese .5
Saltpetre 2
Green Bottle Glass
Quartz Sand 100
Lime 34
Charcoal 5
Salt Cake 38

Optical Glass
Sand 100
Lead 67
Potash 30
Saltpetre 3-1/3

 
 

Semi White Plate Glass
Quartz Sand 100
Lime 26
Charcoal 4
Salt Cake 26

Amber Bottle Glass
Quartz Sand 100
Lime 38
Cannel Coal 14
Charcoal 8
Salt Cake 40

Lime Flint Glass
Sand 100
Potash 35
Burned Lime 19
Nitre 1.25
Green Nickel Carbonate .007
Cullet 100
 
 

Gold Red Glass - 600 lb batch
Measured by weight instead of parts.
Sand 62 lbs
Lead 76 lbs
Nitre 22 lbs
Antimony 6 oz
Manganese 3 oz
Gold 4 oz

Copper Red Glass
Sand 100
Carbonate of Sodium 28
Slacked Lime 24
Lead 8
Cullet 100
Oxide of Copper 4
Oxide of Iron 4
Nitrate of Potassium 8
Cheap Blue Glass
Sand 100
Soda 35
Lime 18
Cobalt 1 (oz)
Nitre 7
Manganese 2.5 (oz)
Arsenic 2.5 (oz)
 

 

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