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lead processing, preparation of the ore for use in various products.
Lead (Pb) is one of the oldest metals known, being one of seven metals used in the ancient world (the others are gold, silver, copper, iron, tin, and mercury). Its low melting point of 327 °C (621 °F), coupled with its easy castability and softness and malleability, make lead and lead alloys especially suitable for a wide range of cast products, including battery grids and terminals, counterweights, plumbing components, and type metal. With a specific gravity of about 11.35 grams per cubic centimetre, lead is the densest of the common metals, except for gold; this makes it a good shield against X-rays and gamma radiation. Its combination of density and softness make it an excellent barrier to sound. Compared with other metals, lead is a poor conductor of heat and electricity, although it has excellent corrosion resistance when it can form an insoluble protective coating on its surface. The metal has a face-centred cubic crystal lattice structure.
Approximately 30 percent of all lead consumed is in the form of lead compounds, such as oxides, tetraethyl and tetramethyllead, lead chromates, sulfates, silicates, and carbonates, and organic compounds. These lead compounds have been used in paste mixtures in storage batteries, in cements, glasses, and ceramics, as pigments in paints, and as an antiknock agent in gasoline.
Lead has been mined and smelted for at least 8,000 years. This is confirmed by artifacts in various museums and by ancient histories and other writings, including the biblical Book of Exodus. Lead beads found in what is now Turkey have been dated to about bce, and the Egyptians are reported to have used lead along with gold, silver, and copper as early as bce. In pharaonic Egypt, lead was used to glaze pottery and make solder as well as for casting into ornamental objects. The British Museum holds a lead figure, found in the temple of Osiris in the ancient city of Abydos in western Anatolia, that dates from bce.
One of the most important historical applications of lead was the water pipes of Rome. Lead pipes were fabricated in 3-metre (10-foot) lengths and in as many as 15 standard diameters. Many of these pipes, still in excellent condition, have been uncovered in modern-day Rome and England. The Roman word plumbum, denoting lead water spouts and connectors, is the origin of the English word plumbing and of the element&#;s symbol, Pb.
Marcus Vitruvius Pollio, a 1st-century-bce Roman architect and engineer, warned about the use of lead pipes for conveying water, recommending that clay pipes be used instead. Vitruvius also referred in his writing to the poor colour of the workers in lead factories of that day, noting that the fumes from molten lead destroy the &#;vigour of the blood.&#; On the other hand, there were many who believed lead to have favourable medical qualities. Pliny, a Roman scholar of the 1st century ce, wrote that lead could be used for the removal of scars, as a liniment, or as an ingredient in plasters for ulcers and the eyes, among other health applications.
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Learn MoreMany churches and major buildings constructed in the 15th and 16th centuries provide examples of lead employed as a roofing material and for water conveyance. Indeed, the stained-glass windows of many cathedrals and castles of this period were made possible by the use of lead cames that held the glass elements together in a magnificent unity of colours and shapes.
In a French physicist, Gaston Planté, discovered that pairs of lead oxide and lead metal electrodes, when immersed in a sulfuric acid electrolyte, generated electrical energy and could subsequently be recharged. A series of further technical improvements by other investigators led to commercial production of lead-acid storage batteries by . The huge growth of battery markets in the 20th century (eventually consuming about 75 percent of the world&#;s lead production) largely paralleled the rise of the automobile, in which batteries found application for starting, lighting, and ignition. Another prominent lead product was tetraethyl lead, a gasoline additive invented in in the United States to solve &#;knocking&#; problems that had become commonplace with the development of high-compression engines operating at high temperatures. Soon after reaching its peak 50 years later, the use of this lead compound declined in the United States as the installation of catalytic converters became mandatory on the exhaust systems of all American passenger cars.
By the early 21st century, China was leading the world in both primary and secondary lead refining. Other top lead refiners include the United States, the United Kingdom, Germany, and India.
OresOf the more than 60 known lead-containing minerals, by far the most important primary ore of the metal is the lead sulfide galena (PbS). Galena often contains silver, zinc, copper, cadmium, bismuth, arsenic, and antimony; in fact, the value of the silver content often exceeds that of the lead, in which case it is deemed a silver ore. Other commercially significant lead-containing minerals are cerussite (lead carbonate) and anglesite (lead sulfate). These are known as secondary minerals in that they derive from galena through natural actions, such as weathering. Cerussite, for instance, is formed by the action of carbonate groundwater on galena, whereas anglesite is formed when galena is subjected to sulfate solutions generated from the oxidation of sulfide minerals.
More than 95 percent of mined lead comes from these three ores. Ores of commercial importance may range from 2 to 20 percent lead or more, even though galena itself contains 86.6 percent lead. This seeming disparity is due to the fact that galena is usually found mixed with other minerals, such as the zinc sulfide zinc blende and the iron sulfides pyrite and marcasite. Consequently, the percentage of recoverable lead in ores is typically about 4 percent, and nearly 90 percent of primary lead ores come as a by-product of zinc and silver mining. More than half of the total lead refinery demand is met by the recycling of spent lead, mostly from reclaimed batteries.
Significant deposits of lead ores are located in Australia, Canada, China, Mexico, Peru, Kazakhstan, Russia, and the United States.
Ideally, a scrum master doesn&#;t need to be in a backlog refinement meeting at all.
In a mature scrum team that has deep experience working in Agile ways and within the scrum framework, the product owner would meet with the development team and seek their help to prioritise the work that needs doing.
Ideally, their relationship would be rock solid and the team could ask questions around each of the proposed backlog items to understand it&#;s purpose and priority and the product owner would be able to ask questions to understand the degree of difficulty of each item and the team&#;s capability to complete the backlog items.
That would be the ideal backlog refinement meeting.
A group of talented, creative, and professional individuals collaborating around product items that are incredibly important to customers and product stakeholders.
But what do you do when you have a young team that are still finding their feet with scrum and one another? How does a scrum master help facilitate backlog refinement meetings with the objective of helping the team become better at hosting these themselves in the future?
For a scrum master, it starts before the actual backlog refinement meeting itself.
You need to invest time with the product owner and help them understand the importance of a healthy backlog. You need to have conversations with them around the backlog items to help clarify their thinking around the item and help them articulate why the item matters to customers.
You&#;re going to help them understand what a good backlog item looks like, what the purpose of each of those items is, and how to communicate with their team.
Remember, many product owners don&#;t have formal training in the role of product ownership and so they don&#;t always know how to articulate their vision, nor do they know how to communicate in compelling and inspiring ways.
It&#;s your job to help them craft the messaging for the team and make sure that they are crystal clear on what they want to achieve and why. The team will figure out how to do the work, so you don&#;t need to focus on that, you just need to make sure they know what needs doing and why it matters.
Product owners often forget that the development team speak a very technical language but don&#;t always speak the business language or understand the business objectives behind the work that needs doing. As a scrum master, you are going to help them with that communication.
You&#;re helping the product owner prepare for the meeting. In some cases, you may need to invite a product stakeholder to the meeting to better represent the problem that needs solving or the feature that needs to be creating. It&#;s your job to advise that if necessary.
It&#;s important that you allow the product owner to lead the product backlog refinement meeting.
After you have prepared them for a successful meeting, you need to give them space to do just that and quietly support the meeting by nudging things along in the right direction if things get stuck or you can see that the team are disengaging on the specific topic.
Your product owner may want to discuss things in a specific order whilst the team may want to discuss those items in a different order. That&#;s great. They can work that out amongst themselves. You want them to be having those discussions and learning how best to work together.
If you can see that there are conflicts, let that come to the surface respectfully and address those issues as a team. It gives people a voice, makes them feel like they have been heard and allows you to address any conflict before it festers and becomes a problem.
If you see that things are dragging on a bit, suggest time boxes to help with time management.
Shorter, sharper conversations that are deeply engaging for the team is going to yield far better results than in-depth conversations that drag on for hours.
If you can&#;t come to a resolution or agreement on a specific item or issue, move on and address it at a later stage outside of the backlog refinement meeting.
It may need more work, different approvals, or just simply need to be broken into smaller parts before the team can agree on what needs doing, why that matters, and how to get it done.
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Structured conversations led by the product owner
You&#;re helping the product owner to lead the conversation by identifying what may be the most important item to discuss and helping them to communicate that effectively to the team.
As they work through their structured items and have meaningful conversations around each item, both the product owner and development team are going to grow in confidence.
Allow them to work out the small issues on their own and they will develop the capability to do that with larger issues and impediments too.
But you want the product owner to be leading these events and conversations with the team.
As a scrum master, you want to be asking questions that help people to understand the nature of the task and why it matters. You want to be provoking conversations that help the team fully understand what is required and, in some cases, how to achieve that goal.
You want a healthy environment where people can bring up any issues they have or ask questions to gain greater clarity and this is where you are teaching the team to have those conversations.
You&#;re creating psychological safety for the team and helping them find ways to respectfully agree and disagree with one another without that leading to unresolved conflict.
As people are heard and in turn, hear the lines of reasoning of others, you naturally find that the team start to agree on what needs doing and how that needs to be done most effectively.
The team are always searching for the right way to build the right product or feature. You are helping them to do that by facilitating the right conversations in the right manner.
You may even be asking the team to decide which skills are necessary to achieve a specific objective or complete a specific backlog item. The team may already possess those skills, or they can make a decision to designate someone in the team to acquire those skills.
You&#;re also going to help the team discuss issues like capacity.
Asking direct questions like &#;what capacity will that backlog item require?&#; allows the team to talk through what is required to successfully deliver the backlog item.
Remember, a backlog refinement meeting is not a one way communication from the product owner to the development team around what needs doing and when it needs to be completed by.
That&#;s project management.
In an agile environment, especially a scrum team, it&#;s a two-way discussion where all members of the team are actively engaged and collaborating toward the best answer or best solution.
You&#;ll find that at times the conversation flows well and at other times, there are lulls.
Wait for those lulls and either provoke more conversation or move to the next step.
As a scrum master, you may find that the conversation has led to it&#;s natural conclusion and the next step is to estimate the size of the work involved.
You can use planning poker or any other methodology for sizing that the team have agreed best works for them. Do a quick group estimate where each individual presents their estimate and you are good to go.
If the team all tend to agree on the size of the problem or product feature, it&#;s a great sign that the team fully understand the problem and have grasped where that backlog item fits in the grand scheme of things.
Sometimes you may have outliers.
One person may choose a 3 and another a 20 when the rest of the team have agreed on an 8.
Have a conversation around those outliers.
Why does one person think it&#;s a 3? What is driving their estimate and what can we learn from that.
The team can either decide that it&#;s worth taking into consideration and adjust their thinking on the estimate, or they can appreciate the input but stick with their original consensus on the size of the problem or feature.
What does matter is that you move to sizing each product backlog item and gain agreement on that estimate. It also matters that the team fully understand what needs doing, why it needs doing, and how to potentially deliver that solution.
In my experience, if you can&#;t size something within 3 attempts in a single meeting its best to put it to one side and move on.
You can always address those tricky items at a later meeting.
Ideally, you want to move through several sizing estimates and get clear on how the backlog should be refined and prioritized.
Look to create timeboxes for items.
It&#;s better to have a short, focused and timeboxed conversation about an item than it is to have a long, meandering conversation that potentially leads nowhere.
Teach the team the value of time boxes. Teach the team the value of having those short, crisp conversations that are focused on the issue at hand.
Let this become the standard they hold for future meetings and embed that ability to move quickly through items in the backlog refinement meetings.
Don&#;t allow the team to get bogged down on a single issue. If it&#;s important, great, we can come back to it at a later stage but for now, it&#;s important that the meeting flows.
Handle one item at a time, complete that item, and then move onto the next item.
Structured, sequential, and focused.
In an hour meeting, if we have 5 minute time boxes then we can address 12 things in our meeting. If we instead look at 20 minute time boxes, then we can only address 3 things in our meeting.
This is where preparation is key.
Knowing what to focus on and why it is important to complete those tasks within the meeting helps facilitate the meeting effectively.
The meeting builds momentum and the team walk away feeling as if the meeting and conversations were productive, valuable, and actionable.
So, in summary.
As a scrum master, step one is to be somewhere else rather than a refinement meeting. If you are needed, step 2 is to ensure that your product owner is ready for the meeting. Step 3, make sure that conversations happen inside useful time frames. Step 4, make sure the team are prompted to estimate the size of items because that prompts deeper conversations that promote understanding.
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For more information on John McFadyen, visit https://www.growingscrummasters.com
See Full BioJohn McFadyen is an Executive and Enterprise Agile Coach with proven experience working on some of the UK and Europe&#;s largest, most complex Agile Transformations. As a Certified Scrum Trainer, John brings a wealth of experience as an Agile coach, Agile practitioner and software developer into each of the four core courses he provides. The war stories, the insights into successful Agile transformations and everything he has learned from coaching high-performance Agile teams combine to provide course delegates with a unique, compelling training experience that transforms as much as it empowers.
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