Commissioning

Commissioning a stained glass window, screen or lamp involves entering into a contract with the designer/maker. It is therefore important that both client and maker know exactly what is involved.

· The price of the work should be established. The materials used in the making of a window, especially the glass itself, can be expensive and the possibility of commissioning a well-designed leaded light should not be ignored.

· The maker will need to know the budget for the work and will provide an estimate, and may require a down payment before beginning work and perhaps payment by instalments, depending upon the cost of the materials involved.

The designer will prepare a preliminary design, according to the client's brief.

· The design should indicate the nature of the construction and the position of any ferramenta or physical support.

· This design should be as detailed as possible. It may be accompanied by samples of the proposed glasses.

· The client must be prepared to recompense an artist for design(s) prepared according to a brief, whether or not it proceeds to execution.

· The copyright in all cases remains the property of the artist.

The arrangements for the execution of the commission must also be satisfactorily established, including those for installation. If necessary, the advice of an architect should be sought; for church commissions, the architect responsible for the church should be involved from the outset. If the window is to be sited in an exposed position or in an area where vandalism is known to be a problem, protective measures should be considered.

Also look at Commission Agreements

Effect of Plaster-Water Ratio on Some Properties

Plaster-water ratio (by weight) 100/30

Setting time (min) 1.75
Compression strength (kg/sq.cm) 808
Dry Density (kg/cu metre) 1806

Plaster-water ratio (by weight) 100/40

Setting time (min) 3.25
Compression strength (kg/sq.cm)474
Dry Density (kg/cu metre) 1548

Plaster-water ratio (by weight) 100/50

Setting time (min) 5.25
Compression strength (kg/sq.cm)316
Dry Density (kg/cu metre) 1352

Plaster-water ratio (by weight) 100/60

Setting time (min) 7.24
Compression strength (kg/sq.cm)228
Dry Density (kg/cu metre) 1206

Plaster-water ratio (by weight) 100/70

Setting time (min) 8.25
Compression strength (kg/sq.cm)175
Dry Density (kg/cu metre) 1083

Plaster-water ratio (by weight) 100/80

Setting time (min) 10.50
Compression strength (kg/sq.cm)126
Dry Density (kg/cu metre) 990

Plaster-water ratio (by weight) 100/90

Setting time (min) 12.00
Compression strength (kg/sq.cm)98
Dry Density (kg/cu metre) 908

Plaster-water ratio (by weight) 100/100

Setting time (min) 13.75
Compression strength (kg/sq.cm) 70
Dry Density (kg/cu metre) 867


This table of relationships makes it clear that the less weight of water added to the plaster, the stronger the resulting mould will be. It also is clear that with less water, the setting time is reduced. So some compromise may be needed to be able to pour the mixture before it sets.

Properties of typical gypsum plasters and cements

Number 1 Pottery Plaster
% of water to dry mix by weight - 70%
Set Time – 27 – 37 mins
Dry density – 1105 kg/cubic metre
Expansion on setting – 0.21%
Compressive strength - 126 kg./square centimeter

No. 1 Casting plaster% of water to dry mix by weight - 70%
Set Time – 27 – 37 mins
Dry density – 1058 kg/cubic metre
Expansion on setting – 0.2%
Compressive strength - 140 kg./square centimeter

Plaster of Paris% of water to dry mix by weight - 70%
Set Time – 27 – 37 mins
Dry density – 1105 kg/cubic metre
Expansion on setting – 0.2%
Compressive strength - 140 kg./square centimeter

Number 1 Casting Plaster% of water to dry mix by weight - 65%
Set Time – 27 – 37 mins
Dry density – 1162 kg/cubic metre
Expansion on setting – 0.22%
Compressive strength - 168 kg./square centimeter

Pottery Plaster
% of water to dry mix by weight - 74%
Set Time – 27 – 37 mins
Dry density – 1162 kg/cubic metre
Expansion on setting – 0.19%
Compressive strength - 126 kg./square centimeter

Hydrocal Cement
% of water to dry mix by weight - 45%
Set Time – 25 – 35 mins
Dry density – 1442 kg/cubic metre
Expansion on setting – 0.39%
Compressive strength – 35 kg./square centimeter

Hydroperm Cement% of water to dry mix by weight - 10%
Set Time – 12 -19 mins
Dry density – 
<641 br="" cubic="" kg="" metre="">Expansion on setting – 0.14%
Compressive strength – 35 kg./square centimeter

Hydro-Stone cement
% of water to dry mix by weight - 32%
Set Time – 17 -20 mins
Dry density – 1913 kg/cubic metre
Expansion on setting – 0.24%
Compressive strength – 703 kg./square centimeter

Ultracal cement
% of water to dry mix by weight - 38%
Set Time – 25 - 35 mins
Dry density – 1568 kg/cubic metre
Expansion on setting – 0.08%
Compressive strength – 421 kg./square centimeter

Break Down Temperatures of Common Mould Constituents

Binders are essential parts of mould materials. They hold the refractory parts of the mould together. Selection is dependent on the temperature you will be using. This also is important in choosing the refractory material to use.

Gypsum plaster - 704C – 816C
Hydrocal cement - 704C – 816C
Hydroperm cement – 760C – 927C

Colloidal silica – 1260C
Colloidal alumina – 1260C
Calcium alumina cement (cement fondu) – 1538C

There are of course, many other factors to take into account when choosing binders and refractory materials for moulds.

Temperature Characteristics of Various Glasses

Over the years I have collected temperature information for a number of glasses. They are of comparative interest and can assist with choosing a temperature or range of temperatures for the work you are doing. If the work is important, or critical, refer to the manufacturer for the latest information.

Bullseye
There has been a lot of information published about this glass. One interesting characteristic has been the different temperatures for the complete range of glass they produce. So there appears to be a difference between the transparent, opalescent and gold pink glasses.
Transparent:
Full Fusing 832C ; Tack Fusing 777C ; Softening 677C ; Annealing 532C ; Strain 493C
Opalescent:
Full Fusing 843C ; Tack Fusing 788C ; Softening 688C ; Annealing 502C ; Strain 463C
Gold Bearing:
Full Fusing 788C ; Tack Fusing 732C ; Softening 635C ; Annealing 472C ; Strain 438C

This also illustrates that not all the characteristics of a glass range are linear. The most apparent one is that the full fusing, tack fusing and softening points of the opalescent glass are higher than transparent, although the annealing point is lower.

Desag GNA
Full Fusing 857C ; Tack Fusing 802C ; Softening 718C ; Annealing 516C ; Strain 427C

Float Glass
Full Fusing 835C ; Tack Fusing ca. 760C ; Softening 720C ; Annealing ca. 530C ; Strain 454

Spectrum S96
Full Fusing 788C ; Tack Fusing 718C ; Softening 677C ; Annealing 510C ; Strain 371C

Uroboros
Full Fusing 788C ; Tack Fusing 732C ; Softening 663C ; Annealing 538C ; Strain 427C

Although the information above may be dated, the important element is that there is little correlation between glasses in the relationship of annealing point to other characteristics of the glass.

This listing also shows that the temperature characteristics are not linear between glasses. For example, Spectrum and Uroboros have the same full fuse temperatures, but different tack fusing, softening, annealing and strain temperatures. Sometimes one is higher than the other, and other times it is reversed.

Another example is shown by the Desag GNA and Float glasses. Desag GNA has higher full fuse and tack fuse temperatures than float, but lower softening, annealing and strain temperatures. This helps to make the point that you need to know the glass you are using as it will not have a proportional relationship at every point in the kiln working temperature range.

I emphasise that these temperatures have been collected over a period and may not be the current or absolutely correct information. They are used here to illustrate the differences within and between the glasses of various manufacturers.

Mesh Sizes

Mesh and grit sizes are most often refered to by a number. This relates to the number of wires per inch - and in a subsidary fashion also to the size of the wire used to form the grid through which the material falls and so is sorted into various sizes. The table below gives some of these figures most useful for mould making - mesh number, percentage of open area, the wire diameters in mm, and the mesh opening or material size in mm.

No.12 ; % open 51.8 ; dia. 0.5842 ; size 1.5240

No.14 ; % open 51.0 ;dia. 0.5080 ; size 1.2954

No.20 ; % open 46.2 ; dia. 0.4064 ; size 0.8636

No.30 ; % open 37.1 ; dia. 0.3048 ; size 0.5156

No.40 ; % open 36.0 ; dia. 0.2286 ; size 0.3810

No.50 ; % open 30.3 ; dia. 0.1905 ; size 0.2794

No.60 ; % open 30.5 ; dia. 0.1397 ; size 0.2337

No.80 ; % open 31.4 ; dia. 0.1143 ; size 0.1778

No.100;% open 30.3 ; dia. 0.0940 ; size 0.1397

No.120; % open 30.7 ; dia. 0.0940 ; size 0.1168

No.200; % open 33.6 ; dia. 0.0533 ; size 0.0737

No.325;% open 30.0 ; dia. 0.0356 ; size 0.0432

Properties of Some Basic Glass Types

Various types of glass have differing properties which make them suitable for a variety of applications. Some of the characteristics of three glasses are given here. The glasses are quartz, soda/lime, and lead crystal.

Quartz glass
Softening point (C) 1508
Annealing point (C) 1048
Strain point (C) 956
CoE at 10-7 metres/degree C: 3.1
Density (kg/m3) 1973
Refractive index 1.459

Soda/Lime glass
Softening point (C) 693 - 732
Annealing point (C) 516 - 549
Strain point (C) 471 - 493
CoE at 10-7 metres/degree C: 56 - 100
Density (kg/m3) 2203 - 2275
Refractive index 1.51 – 1.52

Lead glass
Softening point (C) 438 - 671
Annealing point (C) 366 - 527
Strain point (C) 343 - 449
CoE at 10-7 metres/degree C: 47 - 55
Density (kg/m3) 2505 - 4867
Refractive index 1.54 – 1.75

Creating a Quality Solder Joint

Soldering is the process that uses solder (a metal alloy usually consisting of tin mixed with other metals) for the metallurgical joining of metal components to form an electrical, mechanical or hermetically sealed bond at temperatures (less than 449°C) that are well below the melting temperature of the individual components that are being joined. The soldering equipment (used to create the required heat) and other materials (solder, fluxes, heat sinks, fixtures, etc.) should always be properly matched to the intended soldering application. The equipment and materials used may vary, but the basic soldering techniques that are required will usually remain the same.

One of the most important rules to remember about soldering is "keep it clean". This includes, not only the items being soldered, but also the materials used. Choose quality solders and fluxes without unnecessary impurities. Surface oxidation, contaminants and other impurities are some of the most common reasons for poor quality solder joints. The use of fluxes does not eliminate the need for pre-cleaning the surfaces you are joining, especially if heavy oxidation or large amounts of grease, oil or dirt are present.

1. Clean: Thoroughly clean all surfaces to be joined, removing any dirt, grease, oil, oxidation, paint, coatings or other impurities that may exist before attempting to solder. Proper wetting can only occur when the intended solder joint area has been properly cleaned. Soldering should be performed as soon as possible after cleaning to eliminate the possibility of re oxidation or contamination of the items being soldered. [So leaving pieces fluxed overnight is not good practice. Flux only the area that can be soldered in the next few minutes.]

2. Flux: Apply flux sparingly to each of the intended joint surfaces. Flux is primarily used for the removal of light oxidation and to protect against re-oxidation during the actual soldering process. Make sure you have the right flux for the application being performed.

3. Heat: Apply heat directly to the intended joint area. The correct application of heat is important and should be consistent with the operating requirements determined by the type of equipment being used. Fast and accurate heating will minimize the risk of thermal damage.

4. Solder: Add solder to the heated surfaces you are joining (do not apply solder directly to the tip, or other heat source being used). The solder should flow uniformly over all of the surfaces that are being connected. Stop feeding solder as soon as you have applied an adequate amount and then remove the heat source. The amount of solder is important because too much will create unnecessary waste, while too little can affect the mechanical strength and conductivity of the finished solder joint.

5. Cool: Allow the finished solder joint to remain undisturbed until it has completely cooled. You should never attempt to speed up the cooling process by blowing on the solder joint. Even minor vibrations or disturbances during cooling, can cause micro fractures or other types of damage that may severely weaken the solder joint.

6. Inspect: Check all finished joints for proper wetting, the right amount of solder, a good physical appearance, and the required mechanical strength.

SkillsA quality solder joint is not achieved solely by the equipment and techniques being used, but also by the operator being trained to use them properly. An operator should know how the physical appearance of a finished solder joint helps to determine possible flaws that may exist.

A quality solder joint appears bright, shiny and smooth with all components appearing well soldered. The surface of a finished connection should never look rough, grainy, dull, or flaky (these are signs of what is commonly referred to as a cold solder joint). Problems with proper wetting (solder balling up and not adhering to the components surface) are sometimes associated with too much heat, but are more often related to cleanliness issues.

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Soldering Ingredients and Methods

The soldering process may be accomplished in a wide variety of ways, but the four primary ingredients required will remain the same. They are; the base metal (or metal items being joined) a type of flux (or a method of cleaning and maintaining the surface to be soldered), the solder and a source of heat. It is important to match the soldering method and the equipment that will be used, to the soldering application that is being considered.

Base MetalThe base metal is the metal that is in contact with the solder and forms an intermediate alloy. There are many metals that will react willingly with solders to form a strong chemical and physical bond, while others can be very difficult, or even impossible to solder.

Flux
Flux is used to eliminate minor surface oxidation and to prevent further oxidation of the base metals surface during the heating process. Although there are many types of flux, each will include two basic parts, chemicals and solvents. The chemical includes the active portion, while the solvent is actually the carrying agent. It is the solvent that determines the cleaning method required to remove the remaining residue after soldering.

Solder
Solder is the alloy used to create the solvent action, which generates the bond between the base metals. The type and form of the solder is very important and must be determined by the individual application being performed, as well as the base metals and soldering method being employed.

Methods
There are several methods, as well as a wide variety of tools available to perform the task of soldering. Some of the current methods that are available include induction, conduction, ultrasonic, flame, dipping, resistance, oven and wave soldering. Some of these methods involve the use of small inexpensive hand tools, while others may require large and expensive machinery, equipment and tools. It is a good idea to become educated on the various methods and tools that are available, in order to insure that you are utilizing the best, safest, most efficient and economical means available for your specific soldering application.

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Soldering vs. Welding

The metal joining process that is generally referred to as soldering (or soft soldering) requires temperatures between 183 to 445°C. The joining of metals at temperatures above 445°C (and below the melting point of the metals being joined) is more commonly referred to as brazing (or hard soldering). The actual melting and fusing of the metal items that are being joined together is considered welding. There are, of course overlapping situations that may occur when classifying a process.

The actual joining characteristics that take place are physically different in each of these processes. Soft solders attach to metals by what is referred to as a solvent action that takes place at relatively low temperatures. Hard solders, or brazing alloys contain metals that require higher temperatures to cause the solvent action to take place and fuse the alloy with the metal being joined. Because welding involves actually melting and fusing the surface of the metals that are being joined together, a filler, or fusible material is not always used.

Courtesy of American Beauty Tools