When is a Mass invalid?

For many years now we have only ever attended the Extraordinary Form of Mass. When our children were small we were English Mass Catholics with an intensely traditional outlook. When we moved to Wales we found that the Novus Ordo Mass, as it then was called, was quite different from what we had been used to. There was little reverence, the laity milled around on the sanctuary at various odd occasions during the Mass, children were invited up to sit on the priest's lap while he gave his sermon and much more besides.
After a great deal of soul searching we left never to return. From that day on we only ever went to a Latin Mass and it has held our children (for the most part) in good stead.
Whereas the children of our contemporaries have all with one exception, left the faith (along with their parents).

Part of our rationale was that there was an issue at the time, of a large percentage of British priests who reportedly did not believe in transubstantiation. Now, if what I read today is true there are Bishops and other members of the hierarchy who also now hold to this lack of belief. If the priest does not believe then each and every Mass that he celebrates must surely be invalid? That was our basis for change. There was never a shadow of doubt that a priest who celebrated the Latin Mass did not believe that the bread and wine changed to the body and blood of Our Lord at the Consecration. And that, I believe, holds true today.

If I am correct in my analysis, this does make attending an Ordinary Form Mass something of a lottery. How are you to know whether the priest believes or not?
Well, I tend to observe the outward signs; if the Mass is celebrated reverently and if all liturgical requirements are observed, I am certain that the Mass is valid.
If, however, some or all of the following indicators are in place, my estimate would be that the priest does not believe in transubstantiation and, therefore, the Mass is invalid:-

1. Ceramic chalices and vessels
2. Ordinary bread or wine that does not conform to specification
3. Garish and inappropriate vestments
4. Liturgical aberrations such as lay men and women joining the priest at the Consecration and taking an active role, EMHCs removing or returning the Blessed Sacrament to the tabernacle
5. Inappropriate music or hymns/songs

                                  Photo: BBC
                      A definite no on two counts, earthenware chalice and unleavened bread

Now I stress that these are only indicators of possible invalidity, their use by a priest might render the Mass illicit but not invalid provided that belief existed.
A priest being in a state of mortal sin does not invalidate the Mass per se although it may well be a reason for changing parishes if this is a continual state eg a priest living openly in a relationship with a woman.

Here are the Church's conditions for a Mass to be valid:

1. INTENT: The priest must have the belief as cited by The Council of Trent -

Council of Trent, Seventh Session March 3rd, 1547: Canon 11: " If anyone says that in ministers, when they effect and confer the sacraments, there is not required at least the intention of doing what the Church does, [Eugene IV in the decr. cited.] let him be anathema."

2. VALID ORDINATION : The priest must be validly ordained

3. THE INTEGRITY OF THE MATTER : This refers to the specific make up of the bread and the wine eg the bread must be unleavened and made from wheat

So what happens if a Mass is invalid? Does that mean that transubstantiation has not taken place?

I believe that to be the case but I am sure that someone out there will have a good point to make.